One Hour Layover for IAD to International Flight Sufficient?

Traveling with family (2 kids) on United to Belize, plane leaves around midnight. We have the option of a 3.5 – 4 hour layover or a 1 hour 8 minute one. I know that IAD is efficient for domestic flights but what about Domestic to Int’l?

Any recommendation on whether to take an earlier (midnight) flight with a 3.5-4 hour layover or chance it with a later (5 am) flight with 1 hour 8 min layover? Obviously, the shorter one is ideal so long as it is doable and we arent shooting ourselves in the foot with an aggressive flight itinerary. TIA