For my contests I got sprayed down with ProTan twice - spray, let it dry & sleep over night, take a shower in the morning. Next layer the next night, sleep in it, take a shower in the morning. Maybe a last layer the night before the show. And bring a bottle to touch up with, especially your face so you don't lool like you've been wearing sunglasses in the tanning booth. Then get some oil done by the people who help do the warm up right before the show.
Another guy I know used Dream Tan - you don't' have to do all the pre-spray & dry stuff - but it will smudge if you rub things on it and DON"T use the oil before the show. This guy put it on the morning of the show and sort of looked like he had rolled in oily curry powder during the pre-judge. But after he took a shower enough of it stayed on that he looked great for the evening show. You might play with that and see how it works after setting a while and then take a shower.
And make sure you have a good base tan already!