Rest is not wasted time when exhaustion would have made the next hour useless.

Pushing on through real exhaustion does not add hours, it borrows them from a version of you who will be less capable. An hour worked in that state is often slower, more error-prone, and followed by a longer recovery than the rest would have taken. Calling that hour productive is a bookkeeping trick. Rest that prevents a bad hour has done as much as the hour itself would have.

When you are tempted to keep going tonight, ask honestly what the next hour would produce. If the answer is work you will redo tomorrow, stop. Deciding on that basis takes the guilt out of it.