I believe that TSI closes down at dusk. Sunset in Orlando is about 7:30 at this time of the year so my guess would be that TSI closes somewhere between 6:30 and 7:00. Unless, of course, the park is closing earlier then this.
I should add...I want to visit there before MNSSHP starts. We've skipped it that past few trips and my kids want to go back. I'm hoping if I get there just after 4:00 we can spend a little time here first.