After how many hours should I shift the guys for maximum steriflty effect

Hi, I am working with strain (genotype: daf-2::spe-9(hc88)I; fer-15(b26)II.). I was interested to know after how many hours after eggs are transferred on to the plate, a temp shift to 25 C from 20 C, is recommended to achieve maximum and full proficiency sterility in the offspring. I tried to do it earlier as per papers but when after 3 days I checked, I still found few L1s in the adult population. So, I would appreciate if someone could throw some light on this. I have tried keeping the stain at 20C for 24 hrs, after 27 hrs, and then making the change to 25 C but still they all go into Dauer Arrest if its too early ??? ??? or I f I do it too late sometimes, I still find L1s with the Adult population left. Pls share your views on this. Thanks