On paper, 1000 am looks pretty good. There's a 1030a A320 to DEN, a 1010a CRJ to IAD and that's it for a while; the next departures at a 1240p CRJ to IAD and a 1243p mainline to ORD. The DEN flight should close check-in at 10, and the first IAD/ORD passengers will probably start showing up around 11-1115, so that hour or so should be pretty quiet at the UA counter. Also, from 200p on looks good; there's a 205p RJ to IAD and a 230p mainline to ORD, but no further departures until a 533p mainline to DEN, 529p mainline to ORD, 516p RJ to IAD and a 612p mainline to SFO, so those passengers will most likely start showing up around 400p, so there should be an 2 hour window there as well.