Yes you should reach terminal building at least 1.5 to 2 hours before the flight time
You can do fine with one hour of you know your way around
Also, whoever sends you off can park at the A/B/C Garages for free for 60 minutes.
In most cases, 2 hours is sufficient. If you really don't want to take a risk, then plan 2.5 hours. Traffic is always an unknown in the DC area, so factor that in as well. Good luck!
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