It is good that you are considering the moon phase, but as a beginner your priorities should be focused on the meditations themselves, not necessarily the preparation leading up to them. Avoiding "analysis paralysis" is important, as there is a balance between acting and thinking which should be sought.
Try not to start on a void moon, and that is as far as you need to go with this, for now. Later, you can branch out from the 40 day exercises and that will give you the opportunity to start choosing ideal beginnings for your spiritual actions. For now, any time is sufficient.