I would time your appointment according to your birth date. I found it interesting that our Nexus is valid for almost 6 years. DW and my birth dates are in Sept and Aug. Our Nexus is valid through our birthday 2022. So if your birthday is coming up, wait to schedule your appointment until after your birthday. I suspect they don't want to make your Nexus valid for less than five years after first approval, so timing can be useful.

Of course, if you are traveling in the near future and want the benefits of Nexus, then it is better to get your approval before then regardless of when your date of birth is.