I find that the planetary days and hours have a much more direct impact on spells than the lunar cycle. That being said, if you are smart about it you will look at all of the influences and determine the best time to perform your work. Of course, the phase of the moon becomes much more important when working with lunar deities or energies.
So, let's say you want to do a spell to attract love. Optimally, you would want to do so on the day and hour of Venus, on either the new or waxing moon. If that is not possible, your next best bet is any day during the hour of Venus in the new or waxing moon. Your next choice would be any day in the hour of Venus during any moon cycle.