Q. What is the typical duration between a selection interview and the issuance of visas?
Answer: after an interview is completed (or an interview waiver has been granted), the process usually enters another phase in which the Canadian Government engages in security background verifications and checks.
(Note: sometimes the security background verification phase begins even prior to an interview, but the norm seems to be once the interview is completed, or the interview waiver has been granted.)
Most of the time this security-phase takes just a couple of months. But in other cases it can take much longer.
Also, if you have moved or changed addresses, or there have been problems with local mail service, you may wish to advise the Canadian Government of a reliable mailing address.