How do you spend your time (building vs. marketing/sales)?

I spent the first 3 months just building and taking a bit of time each week to conduct user research. Now after the MVP launch, I feel like I need to keep marketing all the time so that the active user numbers don't drop (theremight be a retention issue).

There's a ton to do on the development side, but the essential functions work. I'm not sure how timely and important the additional improvements are. I don't know what a good balance of my time is.