Summary
The Pull Request (PR) build time is one important aspect of engineer efficiency, and we strive to keep it under 30 mins in the past. A PR task build time is comprised of task "schedule time" and "run time". While the task schedule time depends on the real-time availability of build infrastructure (which tends to be dynamic), the run time is more under control. 

A recent checking of a few PR patch builds showed some unit-test-bucket?? tasks were the longest-running ones, which took over 25mins to run on the Windows build variant. We should use this ticket to rebalance the buckets (or add new ones) to bring down the runtime. It's also worth a quick check to see if some of the tests in there run for longer than necessary. 

Motivation

• Does this affect any team outside of WT?
  (Are they blocked? Are they waiting for an answer?)

No.

• How likely is it that this use case or problem will occur?
  (Main path? Edge case? Frequency of the issue?)

Over 25mins task runtime was pretty consistent in the few PR builds being checked.

• If the problem does occur, what are the consequences and how severe are they?
  (A minor annoyance at a log message? Performance concern? Outage/unavailability? Test Failure?)

It affects the development efficiency. 

• Is this issue urgent?
  (Does this ticket have a required timeline? What is it?)

No, but solving it is expected to improve engineer efficiency. 

Acceptance Criteria (Definition of Done)
(When will this ticket be considered done? What is the acceptance criteria for this ticket to be closed?)

• Testing
  (What all testing needs to be done as part of this ticket? Unit? Functional? Performance?Testing at MongoDB side?)

It's a tests balancing/adjustment work. No new test is expected to be introduced.

• Documentation update
  (Does this ticket require a change in the architecture guide? If yes, please create a corresponding doc ticket.)

No documentation update is needed.

[Optional] Suggested Solution
(Is there any suggested solution to handle this issue? Is it related to any existing WT ticket? Is it related to any previous issue fixed? If yes, link the WT ticket number using related to, depends on, dependent on by links)