Frantic, last-minute over-practicing is about the worst thing you can possibly do. Practice Monster loves it when you cram. He feasts on your fear.
Whenever I have a big performance coming up, I make sure that I am practicing at least four hours per day for the full month before the event. I might schedule a specific number of measures per week, spread out over several months. I try to have the entire program learned the month before, so I can focus on details and stamina in the weeks leading up to the concert.
It is of extreme importance that the basics routine is never abandoned. A long session might be half fundamentals and half repertoire. Bailing on basics weakens the foundation that you are building upon. Would a basketball player only practice dunks during the regular season? Only if the goal is injuries and missed free throws!
The luxury of a long preparation period isn't always a reality, but we can take steps to avoid the frenzy of "crunch time." A practice schedule that includes a solid routine of fundamentals will keep the beast at bay.