I only cut when I see evidence that the eggs are ready. I'll look for little slits in the egg or even better...a head poking out tells me they're ready. I incubate at 89 degrees and over the past 3 season and 24 clutches, 53 days has been the mark. The longest was 55 days and that only happened once. So "when to cut" is really dependent upon your own set of circumstances. One question though, 88 to 92 degrees seems like a big range. What type of thermostat are you using?