"In" is used with expressions of time to express a period, after which something will happen - I'll see you in a week; I'll be ready in one hour (I'll see you after a week has passed; I'll be ready after one hour has passed.
3Expressing the length of time before a future event is expected to
‘I'll see you in fifteen minutes’
In (Oxford Dictionaries)
"Within" is used to express a maximum amount of time, during which something will happen - I'll see you within a week; I'll be ready within one hour (I'll see you no later than one week in the future; I'll be ready no later than one hour in the future).
3 Occurring inside (a particular period of time)
‘tickets were sold out within two hours’ ‘33 per cent offended again
within two years of being released’
Within (Oxford Dictionaries)