Since you are looking to move up to a 6am flight from a later day flight, the challenge is that you will not be able to check until T minus 24 hours of your scheduled flight. So if your flight is at 7pm, for example, you can't check until 7pm the day before. At that point, there may be fewer seats available on the 6am flight that leaves only 11 hours later. As an EXP, you would have priority over non EXPs (except CK) who are standing by for a SDFC. Ideally you would hope to see the option to confirm the seat when you do the SDFC process in app/web site so you don't have to fret over whether you'll be waiting at the gate.