3.5 hours is fine for an EC and I don’t know why folks think it needs to be more, to be valid. OP isn’t applying to join a dance theater. Of course, adcoms will appreciate it, as an activity.
In the past, on CC, when getting to an activity takes time (eg, the kid who rides an hour each way to a metro youth orchestra,) we allowed some of that time to be included. But it can misrepresent to call OP’s dancing 5.5 hours when it’s 3.5. She needs to think carefully.
But to borrow skieurope’s phrase, calling it 3.5 versus 5.5 won’t be what gets her an admit or not.
She could say, 3.5 plus an hour getting there. This point is not a showstopper or major tip factor. Be honest. If it were, say, robotics and getting home took an extra hour on the late bus, you wouldn’t add an hour to the robotics demands.