If you buy a general admission ticket for a thrusday are you still allowed to be inside the museum until 8pm?

Yes, a general admission ticket is good for the duration of the day the ticket was purchased. On Thursdays, your admission ticket would allow access to the museum from 10:30 a.m. to 8:00 p.m.

yes, you can leave and come back, and there is a patio where you can hang out with refreshments

Yes.