On my Panama Canal Cruise and our European Cruise last year they had the Muster Drill the second day. It really is not all that unusual. Sometimes the sailings are simply too late in the day to have the muster around the sailing time.
On both of my southern Caribbean sailings out of San Juan, which sailed at 10:00 p.m., we had the muster drill the next afternoon about 4:00 p.m., once as we left St. Croix, and once as we left St. Thomas. On the Summit Hawaii cruise, which sailed at mdinight, it was also the next day.
The weirdest situation I've ever encountered was on Horizon last November. It was a very late sailing. There was one before sailing and a "make up session" the next day for people who are not on board. Wonder how many of the non-attendees for the evening drill showed up the next day?