You can apply for an eTA at the last minute, however we encourage you to apply at least 5 days before your intended date of travel.

While most eTA applications are processed within minutes, the Government of Canada may request additional information from some applicants which may delay approval and result in missing timely flights.

If you are travelling on the same day when you apply, we highly recommend contacting our office to speak with one of our Client Service Representatives. 

https://blog.traveleta.ca/what-if-i-arrive-at-the-airport-without-an-eta