How early in the year do others start drone rearing. I'm guessing it's a case of selecting the colonies and putting a frame of drawn drone comb in the middle.
You will have to disregard some of the nonsense promulgated by some on queen rearing!
Drone rearing for open mating in an isolated apiary takes place years before with queen selection.
Some it seems are still under the misconception that a that a good last seasons queen will automatically produce good drones.... a couple of frames of drone brood supplied from someone who thinks he has decent whatever bees does not cut the mustard!
Possibly... however the beebreeder needs to look much further back to the parents, grand parents and even great grandparents to select for the qualities required.. this requires good record keeping ( as B+ does with his Carnolians and Hivemaker does with his line of hybrids)
Once your specific colonies for drone propogation have been selected in the previous season... beef them up to double brood... feed and treat let them keep their own stores and do not over inspect!
At the beginning of the season replace the used up stores frames with ready drawn DRONE foundation placing next to the worker brood already being nurtured.
Do the same with any other colonies in you isolated apiary... but use undrawn foundation... this is valuable once drawn out.
Cull drones laid up throughout the season from the support colonies ( ideally you would only have your selected colonies in the isolated mating apiary)
Method has worked well for me in my deep
dark valley where the little birds do change their voices! ( Folk song from Bob Maynard Copthorne Sussex.. Banks of Sweet Primeroses!)
Yeghes da
. Although the competition is fierce in the area with beekeepers at Nunnington, Helmsley and several more in Pickering. Isolated mating is not a feasable option. 
