I'm flying on Thursday from Edinburgh to Ottawa through Dulles (first segment United, second is Go Jet Airlines/United Express). The connection time is 1.5 hrs, but I'm wary of the inbound landing late and am not sure how complicated the connection is. I will have hand luggage and assume I have to go through US customers, put bags through security again, and then make my way to the gate? I haven't flown through Dulles before and have no idea what to expect re transfer time. Essential I get home asap because of childcare so very much not keen on misconnecting.

I have a Nexus card and am Star Gold if that helps with border and security.

From looking online it looks like I'll all be in one concourse area and it should be relatively quick, as long as I don't screw something up.

I think it is possible, maybe even likely that you can make it, given no checked luggage and I think the Nexus card should give you Global Entry and pre-check TSA access after clearing Immigration and Customs. Dulles is normally my destination airport, so I don't have experience in the past decade changing planes there (it is possible to have a long walk to a connecting United gate), but with Global Entry, it is pretty quick normally to be out the door. Worst case, there is a later flight in the evening to Ottawa if your United flight from EDI is late or something otherwise messes up.