Specifically to this event (and as a general FAQ), it should be clearly stated that Quest power numbers, skill effects, event effects, (and any other misc effects) and results, are all locked in at the time of quest launch. This is always the case regardless of an event taking place. The countdown on quest parties is only there to let you know how long until you can collect your results (not when the quest checks to see what effects are present, then give you results).
Many people do not know this. This is why people launch parties before the event starts, see the event trigger, and wonder why the effect of the event doesn't apply to parties already launched.