In reply to Eusum Mudegoren.

Hi Eusum,
There are many different types of moonphase complications and they have different degrees of accuracy. The type that you have will largely dictate best practices as far as setting instructions, but the "standard" variety changes over in a single increment at a set time each day, which means that its accuracy is limited and setting the moonphase to a specific time is not possible.
In the scenario you have where the "full moon" is on Dec.29, and you are setting the watch later that morning on the 29th (say you wake up at 7:00am), you do not need to advance the watch a full month forward, as this would ultimately place you exactly back where you were before (just displaying the other side of the moonphase disc.