Have snow on the ground here into end of March, sometimes as long as into third week of April. When it does change season it does so fast. Timing is everything. A week of heat wave end of April, a couple of days of snow in May, next heat wave (27-30 deg C) mid May. June which is usually wet; sunny in the morning and thunderstorms in afternoon and evening every day for 2-3 weeks straight. July/August are nice (usually) 22 - 28 deg C. "April showers bring may flowers" .... ummm no way, not here. "June showers bring July flowers". First frost is August 25ish.
Knowing from experience the early season annual weather pattern here ... As an experiment I started my first early queens this year really early, around April 14. The hives were still winter wrapped. Still 2 feet of snow on the ground. +6 C days, -6 C nights. It was fairly successful. The logic and the golly guess timing aligned right on the first heat wave at end of April and 1st week of May. The heat wave hit, queens bees and drones filled the skies. Got the Q's mated very quickly just fine. Problem then was after that the hives were bare of drones so the next batch of queens failed to find enough mates. They lingered and over half of them never did mate at all. If I can figure out how to get the bees to bulk up on drones sooner then the early queen rearing could be a more plausible reality here and should be able to yield higher number of queens. I have to get them done early because June is usually wet and a write off, as said. In a bit of a contrast June is also the time of population explosion: aka swarming season here. It is the time for apiary loss recovery and increases, splits. Need to have queens ready ahead of time. April/May queens is possible if there can be more drones.
I get the mite comment and hive health concerns. I do not believe that to be the problem. Hives were and are strong and healthy with mite counts of 0 to 1 per 300 since first checks in March. By alcohol wash method. If they were not healthy, it would not have been possible to have taken 4 full splits off of each of them (using the May queens) throughout month of June. each 1 hive in May is = 4 hive now.
It is all about the drones, much as we love'em for colony balance and mating queens, or hate'em as loitering honey sucking mite traps or whatever. They are the key to this golden locket.