I usually open it to get chicks out every 24 hours after they start hatching. I mist warm water along the sides before I close it back up. The humidity may drop to 60%. It recovers pretty quickly though
I live in hot and humid southeast Alabama. I have best results doing a totally dry incubation for the first 18 days. Then I add some water to increase humidity for "lockdown". My humidity usually runs 28-38% without adding any water at all