Global Entry [0], if you are a US citizen or permanent resident.
It is life changing. Immigration takes under a minute at a kiosk and there is a priority lane at Customs.
[0] https://www.cbp.gov/travel/trusted-traveler-programs/global-...
Even with Global Entry I've had immigration take 25 minutes at O'Hare.
The last time I did this I had Global Entry and 5 of the 10ish kiosks were broken so that took a fair bit of time as well (you skip immigration but not customs in that case).
[edit] the time I had a truly miserable experience the line for immigration stretched long down the hallway to the immigration hall. It took more than an hour to see where the citizens vs non-citizens lanes began.
If one very consistently flies exactly Delta 6 and is a US citizen, one will very rarely wait more than 15 minutes in Detroit.
It is, unfortunately, very, very easy to spend hours in line. (4th quartile for me is probably 2 hours; max was close to 5.) If one is selected for secondary screening, throw all estimates out window; you've transitioned from routine travel into an adversarial proceeding with the USFG.
[+] Since most airlines operate on schedules which do not change much on a week-to-week basis it is fairly predictable that e.g. 10 AM on a Tuesday, and hence $BAR Flight $BAZ's scheduled arrival window, will be busy, given that N flights from abroad arrive near that window.
Ok. But how are they (Solve) going to do it ?
Or is the US entry side of things not part of their product offering ?
A lot of our clients flying domestic, however, still find value in the service especially families and the elderly.
Edit: I see from other comments in the thread that you do this at JDK/MIA by having one of your agents stand in the queue ahead of your customers and then letting them cut in when they arrive. The British in me finds this abhorrent, and there's no way I'd do it.