I would recommend you come to the Blue Lagoon directly from the airport if your flight arrives at 7,8,9 in the morning. Hotel Check-in is not until 3pm and this place will relax your mind a body from the over night flight.
The only problem with St. John's is that...after you've returned back home and you have to get up early for work and battle traffic on the 405...your beautiful pictures from the trip only serve as a cruel reminder of how shitty your real life actually is.
See the long thing on the beach down there? That's actually a ship that was chased down by the Greek Navy after it was suspected that there was "wine, tobacco, and women" on board. Guess they thought this wasn't a good combo!