Use your autistic inflexibility to your advantage.
Pick a time to start studying, and force yourself to do it until it gets built into your routine. Don't even go into the room with the computer during this time.
DON'T pick a time to stop studying. Make a goal for what/how much you want to study in that session, and don't stop until you're done.
Quote:
By the way, when I'm not feeling motivated I can sit on my computer chair for 9+ hours without taking a break, how can I stop this?
Set an alarm to get off your computer.
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Music Theory 101: Cadences.
Authentic cadence: V-I
Plagal cadence: IV-I
Deceptive cadence: V- ANYTHING BUT I ! !! !
Beethoven cadence: V-I-V-I-V-V-V-I-I-I-I-I-I-I-I-I-I-I
-I-I-I-I-I-I-I-I! I! I! I I I