As a minor note, that means if there is a COVID test requirement within xx hours of departure then this will probably be the JFK departure time. Though your miles may very.

Covid rules still change so fast nobody knows what they will be when you fl

More importantly, if doing the same on the reverse flight things are very different.

EDIT: I see flyerCO (who knows much better than me) states the Covid check would be at the documents check at DFW. I will accept that his policy is correct, but I would want to be safe an meet the rules for a single flight departing JFK.