Staff apps are generally replied to within under a week. If you have submitted one and cannot find it, you can private message me on the forums so I can help.
However, it will most likely be in the archived applications sections. Staff apps which have been dealt with are moved out of the general section in a few days.
http://forums.minevast.com/forums/archived.58/
Note : You do not receive a notification when getting a reply to a staff app, this is why you may be led to believe it has not been dealt with.