Inside refere-se geralmente a um espaço físico. Ex: the paper is inside the box

Within refere-se a um espaço de tempo.

Ex: she arrived within one hour

Mas às vezes within é usado também com espaço físico. Bom aí, só mesmo o dia a dia para apreder.

Espero ter contribuído!!

There are a few differences ...

within is a preposition

inside is a preposition, an adjective, an adverb, and a noun

As Guilherme pointed out one predominantly uses "within" when it's about temporal boundaries rather than spatial.

That all said: this really should have been in <a href="https://www.italki.com/questions" rel="noopener noreferrer" target="_blank">https://www.italki.com/questions</a>; , not in <a href="https://www.italki.com/discussions" rel="noopener noreferrer" target="_blank">https://www.italki.com/discussions</a>;.