If you reduce the cooldown timer on leves or let players do them more they will absolutely burn out on leves. I would personally increase the leve timer to 48 hours, especially if Square, and most people, don'tt want leves to be the focus of the game in the future.

Leves are repetitive, extremely tedious, and require more travel time than combat time: AKA, they have most of the qualities that drive players away from games and not towards them.

A better option is getting an alternative way to earn guild marks than only through leves.