According to the rules:
[6.9] A shape-changer is a separate genetic strain of human, with the ability to change into the form of a particular animal.These are not humans cursed with Lycanthropy but are instead some kind of human offshoot with the ability to change into a specific animal form. In DragonQuest, the character may have either Wolf, Tiger, Bear or Boar as their animal form and this is determined randomly.
Though not Lycanthropes (i.e. were-animals) they are sensitive to the phases of the moon. The rules have this to say:
A shape-changer may remain in animal form for one-quarter of the night times the phase of the moon; thus, during the full moon the shape-changer could remain in animal form all night. A shape-changer may remain in animal form for one hour times the quarter of the moon during the day. A shape-changer may make one set of transformations times the quarter of the moon.Unfortunately these statements reflect common misconceptions about the phases of the moon and what the terms 1st quarter and last quarter actually mean. Full moon is not the 4th quarter but instead falls in between 1st and last quarters. The term quarter does not refer to the amount of the moon illuminated but how far through the moons orbit around the earth it has progressed.
Farmer's Almanac has a lovely graphic that shows the phases and their names.
|From Farmer's Almanac website.|
|Moon Phase||% of Night||Day Hours||Changes|
|First Quarter Moon|
|Last Quarter Moon|
From a visual standpoint the moon appears full to the human eye for three days but as the rules split the changes up by quarters that means that the full moon period, for purposes of number of changes and length of changes, lasts for one quarter of the moons cycle or 7.38 days here on Earth. Not an easy number to work with. Of course the moon (or moons) on your world can have whatever period you desire. Using a lunar cycle of 28 days would give you a nice tidy 7 days per quarter. Even 30 isn't bad as you can put 7 days each on the New Moon and Full Moon phases and then 8 days each on the First and Last Quarters. Or vice-versa.
The important thing is to pick some method of determining when these Lunar events take place within your game world calendar so that Lunar aspected characters as well as Shape-changers and Astrologers have a consistent system to work with.