(something) is (amount) within [of (something else)]. My office is within 2 miles of the bus station. The second train departs within 5 minutes of the first train's arrival. It is common to drop the last part. In that case, you would normally understand it to mean "now" for time, "here" for space, and so on: My office is within 2 miles.
Here is the definition of the word within from Oxford Dictionary: inside (something) So does that mean the two words have no difference, and can be used exchangingly? Is there any connotation tha...
24 Within is closer to inside - it mainly refers to something like a building where you are physically in (or inside). In can also mean a state or an organisation, so you can be "in trouble", or "in school" but not "within trouble".
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.
Within is regarded as specifying an upper limit: within two days means maybe today, maybe tomorrow, but no later than two days from now. In is sometimes regarded as more precise: in two days could mean two days from now – particularly with a scheduled event, such as a party. That said, there are exceptions where the word in can be more ambiguous. If I tell my supervisor on a Monday: Boss, I ...