Drakes do hatch on some popular stocked streams, namely in the NC areas of the state. 1st Fork, Pine, Kettle, upper Allegheny, etc.
Drakes are the panacea of hatches in PA, the hatch by which all others seem to be measured. Massive in size and numbers, it can get ridiculous. Short in duration and heavily fished, though. That can get ridiculous too, for many it's more of a pilgrammage or celebration of mayflies than a prime fishing opportunity.
Last week of May, first week of June is pretty typical for PA, plus or minus a week or two depending on the year. It's mostly a freestone hatch on larger waters, though Penns and Big Fishing Creek are world famous limestoners with heavy hatches. On smaller waters like they're talking, it's often overlooked and not so impressive, but can offer excellent fishing.
In any one location, the hatch will last about a week at most, and peak for only 2 or 3 days. But it generally moves upstream, so at the bottom end, it may start up to a week earlier than at the top. And colder streams start after warmer ones. So if you're on top of it and willing to follow the hatch all over to different areas and different streams, you can probably be on them for a solid 2 weeks or more.
Our spring jam is generally timed to precede the drakes, and thus avoid the drake crowds. But we've had multiple times where we've hit the very early stages.