By default, action common event will always play during the follow action.
That's not quite correct.
Despite what the documentation says,
action common event is actually a part of the default finish action, not follow - the default follow action is actually empty. And even though the command is a part of the default finish action, it doesn't technically happen then, either.
Regardless of action sequencing, there are only particular times when the battle scene's event interpreter is checked to see whether it has any triggered events queued up to execute - you can see those timings in the settings for a Troop Event. The follow and finish actions each have their own phase, but events aren't checked until the
turn phase.
Both the
action common event and
common event: x commands will reserve the specified common events to be played at the next timing opportunity; the only difference I see is that the latter checks to see whether an event is currently running, although I'm not sure under what circumstances that would be the case.
If you want something like a message window to happen at a specific time,
@Rethy, you're better off pulling the sequence of code commands from the MV script list and including them as an eval in the action sequence.