
This is what the data sheet says:
"Suppression of heat
A single injection as soon as possible after the onset of pro-oestrus is seen. Following the injection, bleeding, vulval swelling and attractiveness to dogs should gradually decrease and stop within 5-7 days. The time for return to oestrus in the majority of bitches will be 5-6 months on average, but in approximately 3% of bitches the interval will be shorter than 3 months and in 1% it will be longer than 12 months."
I would prefer to wait until the next season naturally, as in effect that is the earliest she would come in after being injected, and possibly it would be longer.