I would like to suggest to add the possibility to set a delay when leaving a PvP area to prevent staying out of bound.

There isn't a delay or anything like that, if you are referring to the Messages Config, you can have it say whatever you wish. If you wanted it to be a TruePVP area inside you will have to use something like TruePVE and set the rules for that.

Let me know know if that makes sense.

Your plugin just create zone? It don't change your "state"? (PvE or PvP)