First things first, talk to your significant other about this. You will end up spending weekday evenings and weekends dedicated to a side project. If you are able to get support at home, then make sure you make the best use of your time (as I am sure you will). The trick is to figure out what milestones you want to hit in the beginning of each week, estimate the amount of time it will take, and spread out the work to each day of the week. Use a calendar or scheduler of some sort because it will keep you on track!
Make sure you and your co-founders have found a product that truly solves a user pain or need. I like to follow the Lean LaunchPad method of interviewing at least 10 potential users each week (minimum). It shouldn't be hard, heck, it is actually very fun because you end up learning things about your product from actual users. Here's the trick that my co-founders and I do: every time we pay for a service (eat at restaurant, buy groceries, etc), we always make it a goal to interview 1 person. Try it out! You will better understand your users AND if you truly have a product that amazes your users, just develop and you will see results. Good luck on your venture!