That's plenty of time. International morning arrivals around your arrival time consist of the following flights:
In this particular order between 8am and 10am.
- Ethiopian A350-1000 - 395 pax
- Emirates A380 - 489 pax
- Qatar A350-900 - 283 pax
- Etihad B787-9 - 290 pax
- ANA B787-9(or -8 on some days) - 246 pax
- Korean Air B777-300 - 277 pax
Between 5am and 7am you have United international arrival bank. But all flights should clear the customs way before any of the other intl flights arrive.
6am Lagos B787-8
6am Cape Town B787-9
6am Guatemala City B737-8
6am Sao Paulo B767-400
6:30am San Salvador B737-8
Copa, Avianca and Volaris arrive between 12 midnight and 5am, so no jam at the customs.
Morning is the only time at Dulles where you shouldn't worry about making your intl to domestic connection