The garages are not ran by Disney. They are ran by Reedy Creek Improvement District. You have up to 3 days after that They will tow your car. It's better if you talk to one of the employees that work there. They can make arrangements for you if you notify them. That's only if you have car problems.
They keep track of what cars are where at 4 am. If its 2 nights or more, they tow. If someone drove there and needed an uber, they would be negligent.
I just asked a cast member friend, and she says 2am. I have also read elsewhere that Disney does tend to tow vehicles which are left later.
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