Since the OP starts off quoting Cal Newport's book "Deep Work", we need to differentiate between shallow work and deep work. Running a startup is a whole bunch

Since the OP starts off quoting Cal Newport's book "Deep Work", we need to differentiate between shallow work and deep work. Running a startup is a whole bunch of shallow work most of the time. Work where you have to get into "the zone" to get it done, that's not 90 hours per week. Or likely even 19.