In and Within
When you are speaking of a space of time in the future, you can use 'in' and “within' according to your intended meaning. If you mean to say that you will come back after the end of an hour, then use 'in'.
Incorrect : I shall come back within an hour.
Correct : I shall come back in an hour.
But if you mean that you will come back before the end of an hour, then you should say:
I shall come back within an hour.
Most Popular Course:Data Science of Harvard, MIT, IBM....
