Look at the following two sentences.

This construction will finish after two weeks.	Bu inşaat iki hafta sonra bitecek.
This construction will finish in two weeks.	Bu inşaat iki haftada bitecek.

And then compare them with the next two sentences.

This construction will finish within two weeks.	Bu inşaat iki hafta içinde bitecek.
This construction will finish in the next two weeks.	Bu inşaat iki haftaya bitecek.

In the top two sentences the construction is expected to be finished after 14 days, and not sooner. In the bottom two sentences, the construction is expected to be finished in at most 14 days, so it might also be finished earlier.

Breakdown of Ödevini iki gün içinde bitirmelisin.