Enrollment upon entry at O’Hare

I’ve been conditionally approved (after like 6 months), and trying to schedule an appointment.

There are literally zero appointments available anywhere in Chicago in the next month.

I am flying internationally in September anyways, so debating just postponing and doing enrollment upon entry flying back to O’Hare.

Does conditional approval expire?

Also, does anyone have any experience doing this at O’Hare specifically?

Alternatively, I am flying into Calgary, and I see they do enrollment upon entry as well. Any experiences there?

Thanks in advance