When the day is artificially constrained, you have a good excuse to get rid of non-critical activities. It's like YC -- "meeting with investors for coffee" (or other good but non-key activities) is always viewed as "a good thing to do", but over the 3 months of YC you have license to tell them to wait.
This only works for short periods of "burst" activities, if it is routine then the waste is distributed more or less equally so you get the same percentage of waste unless you work for very short periods. I.e. if somebody goes to smoke for 10 mins every 2 hours (just an example), then he would be out for 1/12 of time regardless of how many hours he works, as long as its substantially more than 2. If he really-really needs to finish something in 3 hours, he may forgo the smoke break once or twice, but if we take a period of a year, it will revert to regular schedule soon.
