i'd say, no matter what you do, wait until you launch and pull in some customers. if your cofounder isn't tech savvy, i would hope that he's the business/marketer type person who's going to be doing the selling of the product. hopefully he'll be the one donating huge time chunks post-launch in order to make it sell, while you don't have much to do.

whichever you decide to do, stay or go, i'd bring it up with your cofounder. bringing up issues instead of letting them fester can help, if they're things that can get resolved.

if the differences are irreconcilable and you're unhappy, jump ship when the fall is comfortable enough for you.