Hello there!

Some time ago, I implemented the set_expires_in method (#322) and forgot to check whether values ​​of type duration other than seconds could be passed as arguments.

I forgot to add a second parameter to the Period template type, so the duration type with a non-standard Period value couldn't be matched with the method signature.

This pull request adds the missing template parameter and replaces seconds with hours in tests and some examples. Some examples using seconds still remain.