I heard that I should it was advisable to apply to renew your Nexus card about 3 months before your expiry date. I applied online for my renewal on December 9. I just received my conditional approval by email. The soonest that I can get in for my interview is April 11 - two months after my card expires ! If I want to make an appointment at one of the centres that does iris scans, the soonest is June.