Depo can take anything up to a year to come out of your system. Each time can be different for the same person as well.
I have been on it twice, the first time for 4 years and it took 9 months for my periods to return, we came off it thinking we would start TTC within a year or so of coming off it but circumstances changed and when we did get married a few years later I had just got a new job, so I went on the depo again... for only 6 months this time. However 9 months after it running out, I have ovulated for the first time (confirmed with opk's) so for me it seems no matter how long I am on it, it takes about 9 months for me to get back in working order. Between my two times on it my periods were like clockwork and I could also tell when I ovulated (I think anyway I never had it confirmed) so hoping I will go back to that as we are now TTC.
Anyway, although I took 9 months... other people have taken a few weeks or like I say up to a year.
My sister took a year the first time she came off it but then came off it early the next time as she expected to wait a long time again and was pregnant within 3 months.
Good luck I hope you are one of the lucky one's who get back to working order pretty much straight away