It takes as long as it takes and a ton of factors figure in. So, start with honesty, openmindedness and willingness, and if you do that, they will take as long as they need to, no more, no less.
If you skimp on any of the three above, they will either get rushed through faster than is honest, or stall because of unwillingness, so stay open minded.
My first sponsor was a "get er done" sort of gal, and I tried hard to please, but nothing was sinking in, making sense and I wasn't "owning" my step work.
Some steps have gone quickly, others have taken more time, others I've had to go back and rework because having moved on I realized I hadn't really been honest or willing the first time round.
I have found the guidance of step working books, guides and lists of questions to ask myself online to be extremely valuable. That way I am not floundering. Every day I can do some work on my step. Read, answer some questions etc. I don't feel lost and stall and fizzle out this way.