My first app took about 3-4 consistent months (learning was very stop start before that) and that included learning Objective C.
The app is very simple but the purpose of making it was to implement things I had learnt and to get more familiar with the language, SDK etc.
I found a youtube channel that had lectures on Objective C (4-8mins each, about 50 videos) and then some more on Objective C with the iOS in mind. .
I would do these after work, on weekends etc and then over Christmas holidays, did most of the coding for the app. I also bought a couple of books to use as reference
I'm lucky I have a friend who is a graphic designer who took care of the art, logo etc for me.
App was submitted and accepted first time.