This is my situation. After staying for about 6 weeks in small clear plastic cups, I decided to up pot most of the cuttings to a somewhat larger pot. Roots and leaves are showing by now.
The cuttings have always stayed inside a large transparent but very closed container, so with very high RH.
Would it be wise to take the lid off or do I leave it on most of the time?
The room where the plants are in is the kitchen and the air is quite dry, around 35% RH. So I am afraid the leaves will dry out.

You have to do it gradually Stormy. Start by leaving it slightly cocked open for about 15 minutes. Then close it again. Later same day cock it open slightly for 15 minutes. If no ill effects leaved it cocked open longer. Over the course of 5-7 days they should be able to be acclimated to the 35% air. Keep your eye on it though.

Can I also gradually adjust them to lower night temps? Until now, they are used to the 68F day and night. The actual room temp is 70F but since the container is sitting near a north facing window, the temp is lower.

A few degrees here and there is not a problem. It's when you get closer to freezing temperatures when damage can occur with baby plants, still, I would not want those babies sitting in temperatures lower than in the 50's.

The RH is doable, I wouldn't mess with the temp too much until you've got a pretty good root ball going.

I think the magic word here is moderation: moderate temps and humidity. Thanks all!