Re: When to re-queen packages?
I wouldn't buy CL queens except from a source like Webster or Palmer (and they don't advertise on CL). Your best bet should they not have any available would be to make your new hives queenless in mid July and allow them to raise a new queen. Providing weather is good you should get a good mating and it will also break the brood cycle and crash the mite population. I recommend this practice for all first year packages.
If nucs are your goal I would order queens and split the hives into nucs in early august.
Always question Conventional Wisdom.