This question came up in the Online 10-day Retreat Nov 3, 2020, guided by Delson Armstrong. Day 0 was part of a daily 30-minute discussion on the suttas, the Dhamma talk and reflections.
(Slightly edited to improve readability)
Sit for as long as you can. You can do an intention that you want to sit for an hour the first time. And the next time an hour 10 minutes, an hour 15 minutes.
If you have the inclination to sit for longer, that’s always good, that’s always suggested. If you want to sit for longer, do sit for longer.
In terms of pushing, it is not necessarily pushing. Let’s say the body wants to stop, but the mind does want to meditate for longer. You cajole the body, saying: how about five more minutes. Let’s see what happens for five more minutes.
Likewise, if the mind is restless and doesn’t want to meditate anymore, you can sit for five more minutes. Treat the mind like a little child. In that way the mind won’t be pushing, it will accept it, and you can continue on with the meditation.
Watch it here