I renewed early. Because I renewed before expiry they extended the validity by IIRC 1 year past expiry., It took many months for them to approve the renewal, I was renewed without needing an interview.
The new card they sent me expires 5 years from the expiry date of the old card, so there was no "loss of time" by renewing early.
I received an email from the NEXUS program today. In it they state "Existing NEXUS and FAST members who renew their membership before the expiry date on their card will retain membership privileges until they can complete their interview. Please renew your membership before it expires to avoid losing your privileges."