I like your premise, but I think it would make leveling up and getting XP far to easy.

Your idea would be awesome when combined with the NM system. However every mob in the world may be a bit much!

Also it really flies in the face of of the FF community logic of setting up a party camp and grinding out XP quickly.
I know your suggesting bonuses and it does not change this aspect of FF. but you do have to admit it's a staple trademark of FF MMO's.

It probably could work, however I would think they were have to be a cap on the max amount of XP a mob can earn a player, and the times probably should be hours not minutes.