Instance Cooldown

It should be possible to set a cooldown on causing the creation of instances, applying to all players who enter that particular instance.
The simplest form would be just linking the cooldown to the existence of the instance; if it exists, the players involved can't create a new one. However, in this case, if one player continues going back and keeping this instance alive, the other players won't be able to generate a new version for themselves.

Cooldown should be defineable, but it probably shouldn't be less than the lower lifespan of the instance? If less than this, players could theoretically create new instances before the old one runs out.

Cooldown shouldn't always apply, as such.
In the guild storage example, the guild leader shouldn't be able to create more than one storage instance, but this doesn't depend on time; it's that a guild storage already exists.