There is one exception in the SDC rules. If you are booked on a red-eye flight departing between Midnight and 4:00 am, you can do a same day change to the day prior.

Is it really a dumb strategy? If a SDC could be changed to a "Different" day then is it really a "Same" day change? If it was allowed, those with SDC fee waivers could easily just purchase the cheapest fare of the day; usually early moring or late night and DDC (different day change) it to what they wanted. Purchase an early flight if you want to fly a day earlier or a late night flight to fly a day later. Pretty much open for abuse.

There is no fee to change your reservation at any time, although a fee difference (credit or collect) will (usually) be imposed.

There are many datapoints of successful changes to routing, adding a segment or getting a non-stop and claiming it was a Same Day change when in fact it was a "Change" on the Same day of travel and any fare difference was waived.

Yould always book a sepearte reservation on a different carrier as a back-up and call AS to see if an agent is able to change your reservation because you finished your project early, or it ran later than expected. 😉

James