Once you have wiped off the hazed wax you can drive it. Rain, to my knowledge, doesn't inhibit the cure time of carnaubas. Sealants, coatings, hybrid waxes with polymers are inhibited by rain or water period while "curing". From my understanding, rain inhibits the cross linking of the polymers. To my understanding that's not so with natural wax carnaubas. Please correct me folks if i'm wrong here.
In fact, some years ago there were folks who used a "spit shine" technique for straight carnaubas whereby they would wipe off the hazed wax and then spritz cold distilled water on the paint to either hasten the curing or bring more shine (not sure on that). Haven't heard much about that any more and maybe due to carnaubas falling out of favor with all the sealants and coatings available.
Finally, if you have driven the waxed vehicle i would suggest a full wash before adding another layer. I always want the paint as clean as possible before applying any LSP.