Don't have a good answer for you here, but I know there are a few companies that offer SDKs to speed up the process. I've heard of a few people that leverage flutter, but I think ultimately it depends on the type of app that you want to roll out. Neobank, a financial management app, savings app, etc. My guess though is around 6-8 months depending on how much you build yourself vs buy from a 3rd party. Best of luck!