Breath of Clarity

Environmental Project Management Discussion #6

Four priority rules are: 1) As Soon As Possible 2) As Late As Possible 3) Shortest Task First and 4) Most Resources First.

Although the default rule for scheduling is As Soon As Possible, the best priority rule is Minimum Slack First (MSF). Its benefits focus on quality. MSF leads to the best performance which results in the sponsor being satisfied. It also reduces schedule slippage because it strongly considers slack. Further, it is known for having minimum total system occupancy time which helps keep matters simple and efficient. Particularly, it is the rule most soundly using facilities which is important considering facilities are a component of the project that may only be available for a limited amount of the project’s duration such as in the case facility services are being rented. I especially respect MSF because it strikes a phenomenal balance between quality and quickness. The others, such as As Late As Possible being a strategy to defer cash outflows as long as possible, seem to specialize in its benefit while MSF is beneficial in a well-rounded way. It is interesting that the rule with the most balanced benefits also was found to be the best performance indicator.

A firm decides which priority rule to use by examining the project’s conditions. For example, the firm would want to implement As Soon As Possible if it is more focused finishing the project in a timely manner and less concerned with thoroughly conducing all non-critical path elements of the scope. In the case a PM is primarily concerned with gaining a profit and has a particularly patient sponsor, it would use As Late As Possible. In the case a PM wants to show the sponsor progress is being made, it would use Shortest Task First. A PM would also use this strategy if it finds the group is running behind on activity completion and needs to get caught up. Perhaps, a PM may use Shortest Task First if a certain crew of workers is at the site on a given day and there are a lot of activities the specialists can get done through a joint effort. A PM may use Most Resources First if it is trying to be proactive with budgeting and wants to complete activities with large resource demands first. If a PM is uncertain about how a high-stake, due to having large resource demands, activity is going to play out, it may want to take care of the activity first to avoid potential complications down the road. Also, if a PM is unsure whether or not a scarce resource is going to be available later, it is going to want to use the Most Resources First rule to acquire and use the resources now. Moreover, in general, a firm decides which priority to use based upon the resources required by tasks and how resources are allocated over the project’s course. A firm’s decision is grounded in both the project’s overall purpose and needs at a given moment.

My example of a situation involves using the Most Successors rule. For example, in my nominated project, I had to scheduled the construction blueprint to be created early on in the process because there are a number of other tasks, such as ordering materials and requesting permits from the city/county, dependent on its completion. I do not know the size of the materials I have to order until I determine all the measurements. I do not know the content of the permit pack I am going to send in for city/county approval until the blueprint is formed. I also need to promptly get the blueprint done because the sponsor needs to review it before I can move forward. Since the sponsor could have more revisions to the blueprint than I originally predict, I want to promptly have a draft available. That way, there is nothing holding up the plethora of construction execution tasks that are scheduled only after the blueprint plan is finalized.

Comment by Cris Marquez:

Hi Mary,

Great post, very informative. I think taking on the most successors first approach would really help to keep your project organized and avoid confusion in the planning and implementing decision not to mention that tasks are reliant on the completion of other tasks and have the potential of hindering or completely bringing the project to a halt.

Comment #1:

Original Post by Janice Lauria:

Four priority rules include the following:

As Soon As Possible-This rule is the default rule for scheduling. It provides the general solution for critical path and time

As Late As Possible-This rule states that all activities are scheduled as late as possible without delaying the project. The purpose of this is to defer cash outflows as long as possible.

Shortest Task First-This rule states that tasks are ordered in terms of their duration, with the shortest first. In general, this rule will maximize the number of tasks that can be completed in a system during a period of time.

Most Resources First-This rule states that activities are ordered by use of a specific resource, with the largest user heading the list. The assumption behind the rule is that more important tasks place higher demand on scare resources.

The priority that is normally rated the best is the minimum-slack-first rule. This rule allows for the least amount of poor performance, schedule slippage, and minimum total system occupancy time. A firm would decide which priority to use by examining their tasks within certain periods and how they allocate resources to those periods sequentially. Based on their schedule, analysis and examination of all of this, they can decide their priority rule. An example of the “As Late As Possible” priority rule is with procurement. Normally with certain services/softwares that is a pay-as-you-go service that won’t be used until a certain release date, you want to wait as long as possible before procurement of said item/service before procurement to ensure you are not wasting money up front. This allows the project not to be delayed while still getting the service in the meantime and deferring the cash outflow as long as possible (Meredith et al. 2018, 368-370)


Meredith, Jack R., Scott M. Shafter, and Samuel J. Mantel. Project Management: A Strategic Managerial Approach. 10th ed. Hoboken, NJ: Wiley, 2018.

My Comment:

Hi Janice,

Awesome example of the “As Late As Possible” rule. It makes sense for a firm to wait until it is ready to leverage the service before beginning it. I can see “As Late As Possible” being combined with “Shortest Task First”. Perhaps, a firm would want to complete the shortest tasks during the waiting period.

I am interested in the part of the “Shortest Task First” rule definition saying the tasks are to be completed “during a period of time”. It seems the “Shortest Task First” rule always needs parameters to define the period of time. What is an example of how the period of time can be determined?

Also, I can see the “As Late As Possible” rule being applied to a situation of a firm not knowing if it is going to need a certain resource until late in the project.

Response by Janice Lauria:


Thank you. What I found on “Shortest Task First” was that it is dependent on things such as slack time, due date, and critical path. These things will help determine its parameters. And I agree that the “As Late As Possible” rule can be applied to a situation when a firm does not know if its is going to need a certain resource until later on in the life cycle of the project.


Meredith, Jack R., Scott M. Shafter, and Samuel J. Mantel. Project Management: A Strategic Managerial Approach. 10th ed. Hoboken, NJ: Wiley, 2018.

Response by Alexis McClintock:

The shortest task first, or shortest processing time first has a couple benefits. Its functions is to minimize completion times throughout the system. This can reduce the number of job in the system at a time, and can lessen job congestions by knocking out the shorter tasks first. However this rule does not consider due dates, or long job wait times.

Comment #2:

Original Post by Tyler Berry:

Four of the common priority rules are:

As Soon As Possible: this is a more general solution to help with critical path and time.

Shortest Task First: As implied, the tasks that require the least amount of time go first.

Most Resources First: Activities that take the most resources will go take place first on the project schedule.

Most Critical Followers: Tasks here are arranged by the number of critical tasks after them.

A priority not listed above, “Minimum Slack First”, is deemed to be the best priority rule. This rule priorities activities with the least amount of slack to go first. Studies show that this rule accounts for the least amount of slippage. Firms when trying to determine which priority rule to use will look to see which is the best fit for their project. They can use mathematical programming and enumeration to determine their best rule to use.

The projects I work for are software based. In software projects it is common for not all functionality to be deployed at the conclusion of the project. This happens for a variety of reasons: unknown complexity, was not critical functionality, unforeseen cost, etc. Because some of the functionality does not end up being critical we sometimes go with the “Most Critical Followers” priority rule for scheduling. That way critical activities are prioritized.

My Comment:

Hi Tyler,

I am intrigued by the example provided and considered why the commonality is inherent to the software industry. I imagine, perhaps, it is because additional project activities enhancing functionality can be remotely completed. Is that the case? The reasons you explained also sort of made it seem as if perhaps full functionality is never achieved if it is not implemented before the project’s conclusion. In your industry specifically, are activities ever labeled critical at the beginning of the project and then changed to non-critical midway through the project? If so, how would it impact the scheduling?

Response by Tyler Berry:

Hi Mary,

Yes it seems that because projects can be done remotely there can be more spin off projects and leadership is more comfortable with moving some of that scope elsewhere. As far as schedule is concerned because we mostly do the most critical followers first, we do not notice as many large schedule shifts that delay the end of the project. You will see schedule shifts for the smaller activities that are not critical, as some activities get moved out of scope and other activities moved up. And because in the software projects we rely mostly on SME’s to do some of the activities, if they are on a critical activity and their activity is taking them longer than expected, there will be schedule adjustments for their less critical activities.