If I can, the day before. More importantly, I play them hard for a minute or two, pull and stretch them, retune. Play, pull and stretch, retune Repeat until they stay in tune. Always tune up from flat, never down from sharp. As long as I do that, I feel o.k. about playing them right away. Of course I'll check right after the first song. My locking tuners especially seem to hold tune well.
Bill, tgo