The last two years, I've broken down and enlarged my pond in March, which, in South Texas is full spring, and the koi and goldfish are gravid.
Both times, the fish spawned IMMEDIATELY after going into the new pond. (like, the morning after) I think the temperature change and water change, i.e. mild "shock" helps tip them over into spawn mode.
One female spawned, another jumped out during the flurry and died, and the third waited a week and then she spawned.