Is two hours. I had a flight change on my return lhr-ord-dfw in September pop up but because (so the agent tells me "I checked") the time difference is 1 hour she can't push a SWU on a new flight I chose because only 2 hour difference in flight times can she do it.

What is your experience in this?

FWIW for this itinerary my inbound was also changed but by only 36 minutes and (3 hours ago on a separate call) the EXP agent was able to confirm me on a new non stop and forced the SWU to clear.

what gives?

HUCA?