In all likelihood, yes, it ought to be dry enough to paint over without lifting or mixing. To check, lightly touch the paint with a clean brush and see if any paint comes off.
You can speed up the drying time of an underpainting by selecting colors with the fastest drying times, by thinning the paint with turps/mineral spirits or an alkyd medium such as Liquin, and by working in a warm environment.
If you're finding the underpainting is drying too slowly for the way you'd like to paint, consider usingacrylic paint for the underpainting.
