I have built multiple SaaS products. I spend about a month building the first version. I get that out in front of users and continue to build upon it if I see traction and based on feedback. If traction isn't there or it becomes obvious user won't pay, I generally move onto something else.

After the initial prototype, it generally takes another 3 to 4 months to build out a full fledged app that I can offer to the masses. It doesn't stop after that though. There is always more to develop and improve including a lot of re-factoring.

I currently have 4 SaaS products on the market and another one in the works.