My routine is as follows. Two days before the tournament I'll play for 2 to 3 hours, normally like to have some competition, not just practicing by myself. The day before I don't touch a cue. If I have a chance I'll throw a video of a good match in that night before bed. The day of, I like about 20 minutes of warm up time, first rack is just shooting balls in, getting a feel for the speed of the tables and also the rails. Next rack I'll shoot some long shots, some rail shots, and some extreme english shots. Last rack I'll break and play a normal game. After that, no shooting until my match. I'll go through that routine each day of the tournament, but only before my first match. For matches after that I'll hit a couple balls to check for speed and that's it.
Tournaments wear most people out mentally, so why work you brain more than you need to before a match? Save your focus for the matches. I also have found that watching good shooting is almost better than actual practice. Watch it being done right, or when there is a mistake made make note of it. Mental preperation is a much bigger factor than most think it is.