Way to long. First customer took forever. I almost wrote it off. Then I went from 0 customers to 3 in 1 month. A little blogging and google ads is all I've done so far.
All told say 12 months from building it to the first $100. Say another 4-6 months to hit $1000. Obviously its a side effort and I'm not getting rich off of it. But I don't put a lot of effort into it either. If you ignore the development time costs, its pretty profitable right now.
I'm going to start doing some real marketing and hopefully it will start gaining more traction. One thing I still find strange is how customers come in bunches. Nothing for a while then a bunch all at once.
The monthly cost will be a big difference in when you hit your revenue goals. I have an idea I'm toying with right now, that if I implement it and it works, would be $300-500 a month per customer, so I would be able to hit those numbers a lot quicker. But then again it would be a longer sales cycle.
What is your app?
Good luck and enjoy. That first customer is a very rewarding experience.