Consider the task
A set of routine questions may fit comfortably inside a shorter block. Learning a new concept or writing a detailed response may benefit from a longer uninterrupted period.
Consider attention
If you can stay engaged for 45 minutes, there is little reason to force yourself into a 20-minute block just because someone says it is optimal. On the other hand, if you consistently lose focus after 25 minutes, a shorter block may be more realistic.
Consider fatigue
Your available attention changes throughout the day. A duration that works after a good night's sleep may feel too ambitious late at night. Adjust the session rather than treating tiredness as a character flaw.
Breaks are part of the plan
A session length is easier to evaluate when you also consider the pause that follows it. A 50-minute study block followed by 10 minutes away from the desk is a different rhythm from an uninterrupted two-hour session.
Experiment instead of guessing
Try a few structures over several study sessions and compare how much useful work you actually complete. For example, test 25/5, 45/10, and 60/10. The goal is to find a rhythm that fits the work, not to win a timer challenge.
Using TAKE.
Create a few presets for different tasks: a short revision block, a longer practice block, and a break timer. TAKE. makes it easy to switch between them without rebuilding your setup.