Well, in the past, it was a crap shoot because some nights, it would be rented out for a private party. Recently, they changed the opening to 8 from 7, but I hear that it's going back to normal.
I like to catch the whole night every once in a while because the early shows are fun and help establish the story. My mind is drawing a blank right now, but I believe the first library show, the Welcoming Party (with Samantha Sterling, Fletcher Hodges, and Emil Bleehall) starts around 7:45, this is if they've gone back to the normal schedule. Prior to this there is some interaction in the Main Salon with Graves, Pamelia, Otis, Fletcher, Samantha?, and Babalonia I believe. After the welcoming party, the library shows are Radio Broadcast, Balderdash Cup, Radiothon, Samantha's Cabaret, Maid Sing-a-long, and the bon voyage HOOPLA!
Also, I don't know if this happens nightly, but one time, I saw Emil Bleehall in the middle of PI interacting with the DJ and a guest before "arriving" for the Welcoming Party.