Well on the board you generaly move stuff 1 at the time.
So the wording is a bit weird but what they try to say is that you only have to move the carrier if not moving it would cause planes to have no landing zone.
So its not earlier as in an earliers phase but earlier as in earlier in the NCB phase.
The game is already weird in that imo all movement should be simultanious. You cant start moving later and still expect to arive at the same time.
If you first await a combat resolution and then move your going to be later then if you are moving immediately.