I was on the Epic this past February in Haven out of PR. We were in the standard line for security and then once we got through the scanners, there was a Haven check-in desk immediately to our left. The Pam Am boarding definitely leaves much to be desired in terms of aesthetic - it's basically a giant warehouse room. The Haven area had a few rows of seats, we filled out paperwork and they gave us each a bottled water. We waited there while they dealt with the paperwork and checked in a few people before us, and then we got escorted directly onto the ship from there.
(Keep in mind, Feb 2021 we were still doing the at-pier COVID testing and all of that fun stuff - there was no separate Haven line there, either. But by the time all of the testing and stuff was done, I think we were one of the first on the ship around 11am or so.)
If anyone has more specific questions, happy to answer them!