The thing is your powers are based off the wish you make to become a magical girl so it all depends on what your heart "wished for"
Sine homura wanted to redo her time with madoka, she got stuck in an eternal time loop (until rebellion of course)
I did the math about this once. she repeated the same month over and over about 100 times (a little less but we will round up for ease of math sake)
12 months in a year.... 100/12.....
8.3
so approximately a little over 8 years of repeating time and time again before madoka achieved her
form and SCREWED EVERYTHING homura had worked for.
Then I really would have to think though... what would my wish be? what wish would I have that would be worth losing my soul over, risk fighting for my life?
And then you have to wonder how the wish will manifest itself as your powers =O
Lol apologies that anime is something I've been pretty deep in for a bit XD