WCS is the beginning of may if someone at T-line decides to do it...
That said, it can really not that great at T-line in May, it rains a lot. And when it snows and you want to ski, T-line sucks because it's too flat. I mean its ok but not great. You can build jumps. And the airstrip road is generally not even plowed until June and the campsites are a ways back there. It will be real winter camping if you go.
I'd go to Bachelor, when it snows you can actually go skiing instead of poling downhill and when its nice there's a good park.