I don't believe there is a set opening date each year but it usually is open by mid to late June - all depends on how quickly the snow melts to allow the road and camp facilities to open. 2021 could see further delays due to COVID restrictions. Glacier has been great about posting updates on the official park website so just keep checking back there. UPDATE: just announced today - Two Med opens 5/28/21!

I would think contacting Glacier Ranger office or website would be your best bet.