Waxing moon to full moon: make things increase; love, money, luck and so on.
Waning moon to new moon: make things decrease or cast spells to make things go away
some traditions of magick view the moon phases as important for spell casting. others do not (hoodoo off the top of my head)
a love spell to make love increase should be performed by the waxing moon and reach its apogee on the full moon.
a love spell to break up or end things should be cast as the moon wanes
others more knowledgable than I can give you greater details, but you can look at day/hour correspondences if you wish to invoke deities associated with them
venus-aphrodite for example has a her day on Fridays. you can look up her "hour" in the correspondences which will tell you when after sunrise or sunset her "time" is. (nb. youll have to look up the sunrise/sunset time for your local area and make your calculation.) so her time is 7 days a week but her special day is Friday.
I use Aphrodite as an example since you asked about love. she is the goddess I turn to for that and who I am most familiar with.