This, to me, is identical to the concept of "reverse budgeting" (aka "pay yourself first" or "every dollar has a job" in YNAB terms) in the financial domain, but instead applied to the time problem space.
If you assign every hour a job, and you take care of "paying yourself first" by taking into account critical/high-priority time-spend first and then allocating for yourself the liesure time last; assuming that your estimates are correct and realistic and don't forget to include all overhead, you can safely say "hey, I have budgeted away 4 hours of free time today and I can use it guilt-free because I already have accounted for all my critical tasks time-spend."
The reason this is not often done however is because it's hard. Time continuously moves, you can never pause to analyze your usage. And the assumption that "your estimates are correct include all overhead" is really hard to ensure - you need to have excellent time tracking and estimation skills to inform/predict those estimates. And time tracking is too much effort to do manually, so it requires good supporting systems, which require intensive classification techniques, which really don't exist yet.
But I digress. We're basically discussing budgeting, but for hours instead of currency, here.
If you assign every hour a job, and you take care of "paying yourself first" by taking into account critical/high-priority time-spend first and then allocating for yourself the liesure time last; assuming that your estimates are correct and realistic and don't forget to include all overhead, you can safely say "hey, I have budgeted away 4 hours of free time today and I can use it guilt-free because I already have accounted for all my critical tasks time-spend."
The reason this is not often done however is because it's hard. Time continuously moves, you can never pause to analyze your usage. And the assumption that "your estimates are correct include all overhead" is really hard to ensure - you need to have excellent time tracking and estimation skills to inform/predict those estimates. And time tracking is too much effort to do manually, so it requires good supporting systems, which require intensive classification techniques, which really don't exist yet.
But I digress. We're basically discussing budgeting, but for hours instead of currency, here.