If they were virgin queens they still needed to go on mating flights. Everything from dragon flies to birds, and toads to skunks like eating bees. Queens are not as maneuverable and make good targets. There is also a chance the queen went back to the wrong hive. too many things are possible that could go wrong. Along with what Iddee mentioned. I have seen eggs as soon as ten days, and as long as 19 days. If I find no eggs after 24 or 25 days I take other steps to prevent laying workers.. My understanding is, it takes about 30 days for laying workers to develop. Re combine or add brood and bees if I need the extra hive.