1:20hr is a tight connection at IAD? I don't think so.
But it looks like your home town airport is ROC. I was on this flight last month (my last flight of the year).
UA6272 ROC - IAD. We've departed few minutes late but arrived early. Air time was 48 minutes. It was on EMB-175 and I have deplaned in terminal D.
I still had plenty of time to send off my niece who was flying to MUC at 5:30pm from gate C8.
Don't worry. Almost 1.5 hour at IAD for connection is plenty.
If you miss this flight for some reason UA will rebook you on their 10pm flight.