Jonathan - These two hives that you speak of, did they swarm? Old queen missing? If she's gone then there's a good chance that your hives either swarmed or superseded. In either case, the virgin will go on mating flights in about a week after she emerges as long as the weather is good. She will start to lay about a week after that.
Now if you have other hives that you can take a frame of very young larva, even eggs and donate to these hives it won't be a bad thing. That way if the virgins don't make it back from mating you have a backup plan.