The question references two coats of glue. Just for the record, you should pre-coat both the rim and the tire. Many sources that I've seen, e.g. Park Tool and Above Category Cycling suggest two coats on the rim, and one on the tire's base tape.
My understanding is that between each coat on the rim, the goal is to let the previous glue dry out. Park Tool specifically said the base coat needs to dry "completely". It also says that tubular glue contains volatile solvents that have to evaporate completely to let the glue set and achieve maximum adhesion. Thus, it's likely that 24 hours is fine. This Weightweenies poster attested that they let the base coats dry for 24h. Moreover, don't forget that after you mount the tire, the glue is still wet, so you want to wait at least 24h before riding it.
In modern times, my understanding is that glue tapes may allow you to skip the drying process, although users should research first if interested. Professional cycling team mechanics would glue the whole team's wheels at once, so at least having a bunch of wheels still took 2-3 days. Anyway, the extended mounting process is one reason most cyclists have moved away from tubulars - although tubeless clinchers can also be complicated, especially if your setup needs tire inserts (e.g. rough gravel, Paris-Roubaix).