All the Princess ships we've been on have had the muster drill before leaving the port. I like how Princess does it, they assemble you in a lounge near to muster location. It's much more orderly and comfortable (rather than in the heat outside).
Right after the muster drill is the sail away party on the Lido deck.
Was that prior to sailing? Sailaway is scheduled for 5 PM.
ALL muster drills take place before the sail time.
SS Norway (12 times) '85 - '97; Radiance OS 06/01; Island Princess 11/04, Grand Princess 11/04/05, Golden Princess 7/21/06, Golden Princess 2/24/07, Explorer of the Seas 12/23/07, Island Princess 11/15/08