I booked tickets for my trip to Iceland through the Chase website for extra points. As I booked through a 3rd party I did not get to select my seats. Unfortunately, when I called Icelandair to select my seats, the selection wasn't very good. The representative I spoke with told me that emergency rows are blocked off until the check-in counter opens on the day of the flight. I have two questions regarding this:

1) How early does the check-in counter open? The representative told me 3 hours before the flight while the Icelandair website says 4 hours before.

2) How early should I get to the check-in counter? I am flying from BWI to BOS on the day of and my flight arrives at 2:15 while the Icelandair flight doesn't depart until 8:45, so I will be at the airport 6.5 hours before the flight departs. Do people tend to line up before the check in counter opens or will I be ok getting to the checkin counter right around the time it opens?