90 Days After Penectomy Surgery

The form must be filled out within 10 days before the flight. Fill out the Entry Form within 10 days before your flight. What is the meaning of within in these sentences? Is it before 10 days before the flight? or Is it after 10 days before the flight? I.e. 8 days or 5 days or even 1 day before the flight is ok (even the same day as the flight)?

90 days after penectomy surgery 1

I understand that you can say, "within 30 days of receiving your application", but I am seeing more and more "within 30 days after your application is received". Is the latter grammatical?

90 days after penectomy surgery 2

Can you say "within 90 days after"? - English Language & Usage Stack ...

90 days after penectomy surgery 3