Final answer:
Actors should be off-book before the final week of rehearsals, which includes dress rehearsals run under showtime conditions, to ensure they are fully prepared for opening night.
Step-by-step explanation:
An actor should go off-book, which means having their lines fully memorized and no longer needing the script during rehearsals, well before the final three dress rehearsals start. These last rehearsals are crucial as they are run under showtime conditions, simulating the actual performance with the goal of making it look, sound, and feel as if it were opening night. This period typically starts about a week prior to the first performance. At this stage, the director watches with the critical eyes of an audience member, making final adjustments that can significantly impact the success of the production. Therefore, going off-book should ideally happen before this time to allow the actors to fully engage with their characters, interact naturally on stage, and adjust to any last-minute changes without the crutch of a script.