Duration
I sometimes find that a specified duration is unnecessarily long. Take meditation sessions. They can sometimes be recommended for an hour when I find that a good effect is attained in 15 minutes or less. I wonder if longer periods are specified because good timers for shorter periods were rare.
I do find that repeating training regularly is an important practice. I like to pick a time somewhat arbitrarily, one that fits into other plans and activities and make sure I repeat the activity daily. That is often key for me: repetitions, not duration.
One of my favorite books is Prof. Larry Rosenberg’s “Breath by Breath”. The title refers to using breath as a focus in meditation. He cites a time when he and students traveled to a Buddhist monastery in Korea, to experience meditation there. He found that the institution had a tradition of staying awake and avoiding sleep for one entire week. My background immediately makes me wonder if that length of time was first used in order to be long enough to be difficult, to make a physical challenge that would be felt. It doesn’t take much for males to dream unnecessarily big.