I think it cant be done but i wanna be sure
can i set up a hunt group and cfna it to a mailbox ???client wants it to go to vm after
6 rings if no one takes the call

It can't technically CF/NA. But, you can make it work that way. You just set the 'Queue Timeout' for the right amount of time, then enter the Vmail extension for the 'Overflow' destination.

Good luck!