I often take the BA293 which is scheduled to arrive 8:20-8:30pm EST. (note there is an earlier IAD flight which I haven’t taken so the below estimates for immigration may differ)

IAD has a unique setup as the first step on leaving the plane is the ‘moon buggy’ over to immigration. That can take 10-20 minutes.

Then immigration itself. Which, without Global Entry, I’ve found can vary wildly from 5 minutes up to 50 minutes. However, my last 3 trips through there, all within the past 3-4 months, the wait at immigration has been at the lower end of that scale, typically leaving immigration and in to baggage reclaim around 30 minutes after landing.

i don’t check a bag, but travel with a colleague who does, and on each occasion bags have been waiting at baggage reclaim.