Super Smash Bros. melee? ?

SO I found my old copy of SSBM for the gamecube, and I found out everything was erased. I want to get mewtwo and I know you need to play vs. Mode for 20 hours or play 700 matches, so if I leave my gamecube on for that time, and just leave it be, will mewtwo apper? More important, if i lose because I wasn't on if, will I have to wait another 20 hours or what?