I'd say 22-23 more days or so in the incubator before lock down. But to be sure, I'd candle them frequently towards the 20 day mark and watch for the air cells to go slanted, then do the lock down when you see a few slanted cells. In all my hatching experience, Guinea eggs are pretty forgiving if you stop turning a day or so too early, or stop turning a little late, same with not enough RH at the beginning of lockdown. But try to keep your humidity at 45-50% thru the entire incubation, then bump it up to 70-75% for lockdown and you should be ok. And of course if you see a pipped egg... it's definitely time for lockdown and higher humidity!
Good luck! Post pics when they hatch!
*Start candling on what you think is day 20 of being in the incubator, and then keep a close eye on them/candle them frequently after that point.
My eggs typically hatch on day 26, and there's sometimes a few stragglers on day 27. Rarely do the hatches last thru day 28... but not everybody's eggs do what mine do!
Edited by PeepsCA - 4/6/12 at 3:55pm