Two hours is the rule of thumb. But if you want to risk it, check the airline's policy for checking bags/checking in for international flights and make sure that you at least beat that. They can be pretty strict.
I agree with Phillip, two hours before your flight.
Two hours
3 hours for an international flight & 2 hours prior to domestic... sometimes you may save time
If you did online check-in and your flight is small.. min you need 1:30 mins in Boston airport..
International entry process is not busy at that time. . Relax..!
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