New to Depo, how long to see effects?

[bbbkmc]

I'm trying Depo on two mares for the first time. Got tired of Regumate and all its handling issues.
How long will it take for the shot to start working?

[tbemoll]

It started working in my mares within 2-3 days of the shot. Lasted 4 months with one mare and 2 months with the other.

[bbbkmc]

One mare seems to be fine, the other looks as if she's coming in season 4 days after shot(and she's been a little minx) ? I take it that means she needs to go back on Regumate, but now how long to wait?