Meaning of "within" in this sentence:"The form must be filled out within 10 days before the flight"

I am a bit confused with the following statements (and I have met these often the last two years):

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?

1. Is it before 10 days before the flight?
or
2. 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)?
• IMO it is ambiguous. Commented Sep 16, 2022 at 22:57

Within sets a limit of range. It means

occurring inside (a particular period of time) (OxfordL)

The particularity of your sentence is that this period of time ends before a certain point in the future. Hence the confusion. Within + range of time + before a certain point in the future basically means not earlier than the beginning of that range.

In your case therefore you can fill out the Entry Form 10 days before the flight, not earlier. But it gives you a range that goes up to a few minutes before the flight. Within that range you are allowed to fill in that entry form.

Maybe it is easier to understand in we picture it like this:

While it's potentially ambiguous, as Weather Vane said, to me it certainly seems more likely to mean "Fill out the entry form no earlier than 10 days before the flight"; I think it's fairly unlikely it was intended to express "at least 10 days before the flight".

As fev says, "within" pretty clearly means that there is some range of time in which you must fill out the form. The potential ambiguity is because in "within 10 days before the flight", the following noun phrase "10 days before the flight" has a form that would generally cause it to be interpreted as a point in time rather than a range. To determine which range of time is meant, it makes most sense to me to take the flight itself (or the date of the flight) as the other point, giving a range "from 10 days before the flight up to (the day of) the flight". The other interpretation would only be possible if you interpreted the other point as the current time ("from now up until 10 days before the flight") which doesn't seem natural to me.

I just spoke with someone with the State Department about something which can only be requested when one is

traveling internationally within 14 calendar days.

Their interpretation is

start with the travel date and count back 13 days and that is the first date on which you can make the request.

For this case, within means less than. So if you were traveling on the 14th, the first date on which you could make the request would be the first. And so if the rule was "within one day" that would mean on the day of travel. Strange, but no sense in arguing.