This was my first real large scale perspective map of this sort.
It took me longer than it should have. I can do them faster now, after having done more of them.
It was a bit daunting when I started it. I think it took me 3 weeks to do.
However I was also working on 3 other map commissions at the same time so it would be hard to say how long exactly it took.
The best way to improve is just to start doing it. Do one. Then another. You get better each time.