The text on the website is a mess - the headline for instance says "If you purchased a seat in Delta Main or Delta Comfort, you can switch to a confirmed seat on a new flight based on availability in your originally purchased fare class" whereas the expanded eligibility section still says "If you are traveling in Delta Comfort, you may make a Same-Day Confirmed change as long as a seat is available in Delta Comfort."

Has anyone actually experienced the new earlier-flights-only restriction since April/May? I have not really been paying close attention since the DoD change flights screen is now a mess of all possible and impossible SDC/SDS and paid changes lumped together (and often wrong and inconsistent with OLCI), but certainly in at least one case this summer I SDC'd to a later flight without problem.

It looks to me like the primary purpose of the website update was to shove in all the new Delta Main Extra Experience verbiage - perhaps someone was lazily copy-pasting while doing that and not intending to change policy. Or perhaps the new policy kicks in in October once refundable tickets get free SDC bundled in.