how long to leave smack pack

hey guys, i'm getting ready to brew this weekend and have a question about using a smack pack. i've never used one before. the brewing instructions that came with the recipe kit say that the smack pack could take anywhere from 3 hours to a few days for the pack to expand. my question is this: will it hurt if i smack the pack a day or two before brewing? or could the pack explode? i would hate to count on the pack only taking a few hours to expand and have it take a day or more and then not have yeast ready when i need to pitch.

any advice would be great. thanks

Smack the night before.. Make sure it's completely broken... Then let it sit at room temp until ready 2 days is too long and 3 hours is assuming its manufacturing date is less than a month

Smack it 4 hours before and relax.