Probably until next year. If the male mated with the females even once, than she will store the sperm and use it for the rest of the season. So unless you can easily tell apart the offspring of each male, I wouldn't do it because there would be no way to know which male is the sire.
I have done it during the season on rare occasions. In fact, I did it this season. During my second breeding season (10 years ago now!) I had paired a SHCT with my Tremper albino in my quest to make hybinos from "scratch". I was getting nowhere with her (4 infertile clutches) and finally in desperation paired her with another gecko and she produced 3 offspring, definitely from the second male.
This season, I had an eclipse het Tremper paired with my tangerine het Tremper male. He developed a prolapse and ultimately needed a hemipenis amputation, so he's currently by himself. She laid 2 infertile clutches. I paired her with my Tremper albino snow het eclipse and she just laid a fertile clutch.
I feel that if there have been several clutches from one male, there's a good chance that introducing a second male will result in offspring from that second male. I do agree that it's best to pair with a male such that you'll be able to tell which male sired the offspring.