It's the most up-to-date version of the schedule and reflects what shift start times that the time clock recognizes. However, if it is different than the wall schedule, you can pretty much go by whichever version is more favorable.
Online schedule randomly has an extra shift in there? Come on in and nobody will say a word. Or if you can't make it, call up the store and tell them to check the posted schedule.
Hours get slashed mid-week? Go by the posted schedule, and point it out to the TL if your punch in is rejected.