Character Groups and associated Cecil's Tasks

I'm confused by this info. Who do I need to keep available and when? I need to take advantage of the event currency earning tasks such as the corn one. But those who can do it are tied up for 16 hours. Something I don't want to ruin myself by having them on it when they need to be on a cecil task. I'm already 2 days behind because the game wasn't updated despite me having google play set to auto update TSTO and no popup about the update.