It is advisable not to exceed 20 minutes. You practice 20 minutes, you stop 15-20 minutes you again 20 minutes, you stop 15-20 minutes you again 20 minutes, etc ... Because telekinesis requires a lot of vital energy.
Personally I practice 20 to 30 minutes, I stop 15 to 20 minutes, I start. I practice three to four in the morning session, for a total of two hours. It depends if I have the energy that morning. When it's good I'm doing longer sessions but then at the next meeting, I have no energy. It's like a test, it is better to study a little each day earlier than three hours on Saturday. The 20-minute sessions you are allowed to keep and not lose all your energy.