Welcome Back Tammy!
Sounds like you have an action packed evening planned! I love it!
I checked the online calendar for Disney's Hollywood Studios (DHS) for
August 13, 2013. They are currently showing Fantasmic! at 9:00 p.m. and 10:30 p.m. so that gives you a little more time. In my opinion, the second performance of Fantasmic! doesn't typically seem as crowded as the first especially when the performances are later. Many Guests have little ones that come to the earlier shows so they can get to bed earlier. That doesn't mean it won't be crowded so I'd still plan to arrive at least 45 minutes prior to showtime.
Here's something else I've noticed about the second performances. It seems they may not start seating as early as they do for the first performance for the evening. That may be because it takes time for them to clear the Hollywood Hills Amphitheater and clean it before they start seating for the second performance. That's just my guess but it can cause a massive line of Guests down Sunset Blvd which causes Guests to stress a bit when they see it. Don't stress. The Amphitheater is huge.
DHS is scheduled to close at 10 p.m. on 8-13-2013. However, you will find the larger shops along Sunset Blvd and Hollywood Blvd open as you make your way out of the park following the last performance of Fantasmic! that evening. I can't resist a final souvenEAR!
Keep the questions coming! We're hEAR for you!
Wishing you minnie magical memories :-) Allison V.