Keep in mind with log shipping the databases aren't in sync unless there are no changes on the primary after the last log backups is sent to the secondary. When the log backup finishes, there is time involved in copying the log, waiting for the restore job to fire, then restoring the log. If anything on the primary changes, then you're out of sync.

This is why Database Mirroring and Availability Groups were created, to give more real time movement of data.