Fixed daylight savings issue when scheduling with offsets

Instead of adding seconds for whatever reason, we now just add
the period itself. This is aware of daylight saving changes and it
will ensure the message will be delivered at the given time.
This issue was caught by the unit test at my local machine, since
the daylight savings time change is now within a month.

Change-Id: I4959c3b2bb3dbf4a2c96beaef6bf0eb02552ff71
Merge "Fixed daylight savings issue when scheduling with offsets"