For me it took a week or so for my "Conditional Approval" to come through. Some people report here that it took 2 business days or less. The NEXUS website claims that it could take as long as 3-6 MONTHS, depending on the complexity of your case.

Basically, it takes however long it takes for CBSA (Canadian Border Services Agency) and CBP (U.S. Customs and Border Protection) both to go through your immigration and customs records and make sure that you are a "low-risk" traveler, AND to clear you through the appropriate background checks of both governments. If you have a complicated travel history, or have convictions, arrests, or other police/government flags on your record (especially immigration/customs violations), it will take longer for Conditional Approval to come, if it comes at all.

After Conditional Approval, you will need to schedule an interview in person at one of the many NEXUS enrollment centers (or "centres," if you're in Canada) . You will need to bring evidence of citizenship, proof of residence (utility/property tax bill), and the letter showing your Conditional Approval. You must schedule the interview within 30 days of receiving the Conditional Approval, but the interview itself can be beyond the 30-day window.

NOTE: If you want to use your NEXUS membership at the airport kiosks in Canada (to enter Canada and for preclearance back to the USA), you MUST visit an enrollment centre at a Canadian airport to complete the iris scan. The US-based enrollment centers do not have the iris scanning equipment. If you prefer to visit a US-based enrollment center, you can get the card valid for land and sea travel, and then you can add on the air kiosk part at your convenience (the next time you happen to be at a Canadian airport featuring an enrollment centre).

When you go for your interview, you will get a fairly stern talking-to from the examining officer. The officer will explain that the penalties for smuggling and/or improperly declaring goods will be much more severe for you, given your "trusted traveler" status. Your fingerprints will be checked against U.S., Canadian, and INTERPOL databases for any activity that might be of interest.