How far has corporate brainwashing taken people that they actually start believing this is a normal way of thinking about time management.
In the situation of a single person startup then you need to be smart about where to put the time and effort, rather than burning yourself out by overworking.
Since who will sustain the effort in the long run if you wont be able to?
It doesn't matter what the reason is, but you're not getting anything done in that time. Why should you consider that as a time you worked during?