There are two conventional wisdoms as far as I've heard about when to raise queens, and also replace them. Spring, and fall. As was stated above, spring is often a typical time because things are just getting started again, they are building up the hive, and there is time to tweak things if they go wonky.
Fall is often the choice because, as was also stated above spring has storms, bad weather which can screw mating flights, if that happens, build up can be delayed seriously very easily,etc,etc,etc. Fall however is after large build-up (You can check the cycle and should know it for your area anyways frankly.) you also allow the strong (Hopefully) old queen build up continuously which builds up the hive population without a break, and is able to capitalize on early flows if you have them as well as later flows/etc. Always great to have a hive built up in timing with the flows of your area, surely. However, if something goes wrong late in the season well then you can be screwed really easily and can run out of time for the winter transition, or the fall storm seasons roll in, let alone the cold comes early.
I typically raise in the spring, keep in builder hives during the summer, know if it is a good layer or not, and replace or not depending on factors of if it is a productive one year queen, or replace if it is a second year queen regardless, and do my joins in the later part of the summer. If you requeen, and join you will have a jump at first, because you are joining, but then you will have a slight dip but population will usually stabilize in about 37 days. and around oct, or so drones will decrease as the hive slims down for winter.
Using the OTS system, purposely moves the peak hive population into a later period to offset Mite peak times later into the season to where before they can peak enough to weaken a hive for the winter, they remain lower as the drones are lessened and thus lesser mite #'s. they are then hit again when drone production is ceased completely later.