I can't really say how it
should or
should-not happen (a lesson which took me Four Years to learn
), but I can say how I've imagined it works in a pending story/comic I'm working on.
In my story ("Oscar County" ... formerly "Pack Mental(ity)"), there are actually two distinct kinds of Werewolf, but I'll focus on just one.
Once a person becomes this kind of Werewolf, their body begins to produce and build up a special kind of chemical/protein/hormone/enzyme/etc. which is used to actually fuel the transformation. As it so happens, the average werewolf builds up just the right amount of this substance in their body in roughly exactly the same period of time as the cycle of the Full Moon.
Once their blood and cells are saturated with this substance, they are primed to transform as soon as an appropriate trigger sets the process off. It just so happens that the Full Moon acts as such an instinctive trigger in their mind when they see it, or even are merely abnormally aware of it's presence, visible or not (such as if they are fearfully, or anxiously anticipating its appearance).
Now theoretically, with this kind of werewolf, if they were separated from any visual confirmation of a Full Moon long enough, (such as being locked indoors for months, or at/near one of the poles where it may not be visible for long periods of time ... assuming it works that way), eventually their transformation cycle would de-synchronize with the cycle of the moon, but still occur in roughly one-month intervals, coinciding with the build up of the substance in their body. ... and maybe some individuals would build it up faster or slower than others ...
To get a little more detailed and specific, this kind of werewolf can not transform if they don't have enough of this stuff stored in their body yet, and if they try to transform early (such as only two weeks after their last transformation, with only 55% of the needed substance) it will be extremely painful and slow, as their body will effectively have to attack itself to draw out the needed materials, and it would not go smoothly at all, like an engine running without oil (much like their very first TF).
Inversely, the longer they put off Transforming, the harder it becomes to resist. If a Werewolf were to avoid letting the sight of the Full Moon trigger a TF, and resisted as long as they could, within a week after the Full Moon (Or roughly One Month + One Week or so, depending on the individual and how fast their bodies produce the substance), they would be so on edge, like they were hopped up on a gallon of strong coffee, and adrenaline, that even stubbing their toe on the bedpost would be enough to set them off and make them
Wolf-Out.
Additionally ... if a Werewolf
really, really needed to make sure that they DON'T transform during an upcoming Full Moon, they could force it a few days early, and therefore be too drained to do it again when the Full Moon Rises. On the other hand, if they knew they wanted to transform on a certain day other than one of a Full Moon (an activity that is a BAD idea, even if they have exceptional self - control ... but simply theoretically speaking ...) they could make a conscious effort to delay or set off their TF early/late the Month before so they will be ready again a week early or a week later. It would take several months preparation to off-set it further than that, unless they are willing to endure excruciating pain. (Though it is at least somewhat painful, no matter what).
... that's how it works in my story anyway ... (though I'm considering modifying it a bit so they can change all three nights of a Full Moon)
The other kind of Werewolf is of purely mystical origin, and therefore is strictly bound to the cycle of the moon as an irresistible command, no matter what, visible or not ... "
resistance is futile". (Unless they are bitten by the other kind of werewolf, which overrides the 'Fake' lycanthropy ... but that's getting off topic)
That's my take on it anyway.