It dosn't matter.... and that's not as stupid at is sounds.
The top of page 6 of my datasheet says: The day-of-week register increments at midnight. Values that correspond to day of week are user-defined but must be sequential. i.e if 1 = Sunday, then 2 = Monday etc.
They just increment the day of week at midnight and when the value is 7 at midnight, they just set it back to 1.Do one thing each day that scares you – work here !