Describe the feature enhancement
We are using the thorough mode in our Validate Process. At the start of a typical day the first PRs are fast as only the newest changes are validated. However, throughout the day the PR validation gets slower and slower. This is because the validation org was created at midnight and tests the same functionality that was merged to master and built successfully earlier the same day.

We are Replenishing the Validate Pool at midnight, 10, 12 and 14. If Validate always used the newest scratch org in the pool, it would mitigate some of this slowdown as it would already contain the latest changes from the same day.