Teams get a maximum of 15 spring practice days, including the intra-squad game that typically caps a spring slate. This doesn't include sessions when players are limited to the film room or the weight room. Everything has to take place within a 34-day window, but spring break and exam days don't automatically count toward that. So some schools spread spring practices over a month and a half.
I can't find an exact date, but it will be late March at the earliest.