Rigid schedules are good if the things you plan are the things that you actually want to spend time on. Time allocation guarantees that you'll work on whatever is scheduled and a side-effect is that it forces you to be be more effective.
Knowing how big part of your day will play out is a very powerful thing. It removes so much stress and uncertainty.
In the end of the day it's a question of balance. It's probably unhealthy to plan every single hour of your life in advance (which Marc does not do), and the same goes with allowing too much spontaneity.
Where as a nun perhaps doesn’t have wealth but has power over their time.