We have done this often and only one time had to wait until our PS time.
I apologize for being early, and the response has always been they rather have us arrive early than late.
We arrived 15 mins early for a 6:30PS time at H&V, not really planning on being seated earlier but decided since there wasn't a line, we just might get lucky. After waiting 10mins for the hostesses (3 of em!) to chat-it-up with 2 guys in front of us who didn't have PS's, they gave us a seating time of 6:40-6:50. Imagine my dismay when the 2 guys were seated at 6:30!
Luckily we only had to wait till 6:35 but upon entering the restaurant, I noticed most of the tables were set for 4.. the size of our party. And those gents were seated at a table for 4.
I asked to speak with the Mgr and she explained that basically it is first-come/first-served even with PS's. Since we had PS's, if we had been written down first then we would've been seated first. I kindly explained that that wasn't possible because the hostesses were too busy to acknowledge any of the line beyond the 2 gents. She then apologized and said she would be speaking with them
My DW and I are early for everything -- well, almost everything. We often get seated right away ... especially if we have that "we're so hungry we could eat a ________" look in our eyes!