RaF invite reset?

Hi all,
so I am wondering has anyone noticed how often the invite a friend resets? If memory serves me, each account has 5 invites to refer-a-friend (at work and so not able to log into Battlenet). I am thinking this is not 5 invites for life and so I am wondering when does this reset?
Anyone tested this?
Just curious more than anything though :)

you got unlimited invite but can only send out max 5 at a time
once the referee ACCEPTS your invitation and opens an account you get a new invite again