Originally Posted by MSPeconomist

The normal rules are you're allowed 24 hours (including overnight) as a connection on an international itinerary but only 4 hours for domestic travel before the "layover" becomes a stopover probably requiring a higher fare (and using multicity search to book the ticket on delta.dumb, although I usually need to call for overnight international connections too). Due to COVID-19 schedule reductions, the 4 hour rule was increased to 6 hours, but IIRC it's now back to 4 again.