I just called UA to inquire about changing my flights from BKK to one day later. The agent simply recommended that I call in with this request 2 hours before my current departure and request the change to the following day as an SDC without charge. She acknowledged this was technically more than 24 hours in advance of my desired new flights, but that agents would bend the rules in such a case.

Does anyone have recent experience with SDCs where there is only one UA flight per day?