From what I can work out with my conversions this seems to be temperatures = days roughly?
@ 30c /86F = 65 to 75 days
@ 30.5c/ 87F = 60 to 65 days
@ 32c / 89.6F = 55 to 60 days
Does that sound right?
(it would be really good if we had one point of reference for this information for all temperatures on the site, just an idea.)
I guess the range is due to minor temperature inaccuracies, fluctuations and position affecting minor differences in temperature, like eggs on the top being hotter and inaccuracies in thermometers.?