I'm only a newbee, but after one of my hives requeened itself in May and fortunately got mated and kept 3 frames both sides half full of brood right thru the winter, and is going like crazy now, I think I will requeen about April so there are lots of young bees to go thru the winter and they fire up as soon as the weather warms. I'm about to try grafting as soon as we get some drones flying, (to do some splits,) so if I get new queens out of that I will leave them until April 2014 unless they are under performing. (Near Wagga, a bit colder than Melb)