The main factors on time are; what day of the week are you leaving, what airline are you flying on, and what time of day is your flight?
Saturday is the busiest day for flights, with Sunday being second. Wednesday has the fewest flights.
Today (Sun 6/15) there are 6 flights leaving for the US between 2:00pm and 3:00pm. That's around 1200 people.
Considering that two of those flights are American, I would definately get there early.
If you're on one of the first flights out, you can probably shave some time off your arrival at the airport.