Exhaust abilities can be activated any time you could normally activate an ability.

You may spend the four mana added by the first ability on the same ability or on multiple abilities.

If an exhaust ability of a permanent is activated, and then that permanent leaves the battlefield and returns to the battlefield, it becomes a new object so its exhaust ability can be activated again.

If an ability triggers whenever you activate an exhaust ability, that ability resolves before the exhaust ability resolves.