While all spells and rituals can work without proper timing, it's best to try them during specific days of the week and during specific phases of the moon. Of course, you can also attribute astrological timing, time of day, and likely many other time related lineups in spellwork, but this is just a basic reference or foundation.
Sunday: Sunday is named after the Sun and represents Gods like Apollo or Helios. This day is typically reserved for solar power, spirituality, empowerment, success, health, vitality, generosity, material wealth and invoking the God's aid.
Monday: Monday is named after the moon and represents goddesses like Diana or Selene. This day is typically reserved for lunar power, spirituality, cleansing, purity, unity, psychic ability, magick, change, childbirth and invoking the Goddess's aid.
Tuesday: Tuesday is named after the Norse God Tyr, and is represented with the planet Mars or Ares. This day is typically reserved for physical energy, vitality, strength, passion, motivation, sexuality, movement, intensity, drive, ambition, achievement and men's needs.
Wednesday: Wednesday is named after "Odin's Day" in old English, and is represented with the planet Mercury or Hermes. This day is typically reserved for knowledge, communication, mental arts, charm, confidence, change, adaptability and acceptance.
Thursday: Thursday is named after the Norse God Thor, and is represented with the planet Jupiter or Zeus. This day is typically reserved for luck, growth, expansion, honor, attainment, power, influence, accomplishment and fulfillment.
Friday: Friday is named after the Norse Goddess Freya, and is represented with the planets Earth and Venus (or Aphrodite). This day is typically reserved for fertility, money, prosperity, healing, hope, sharing, bonding, grace, charm, goodness and women's needs.
Saturday: Saturday is named after the God Saturn and is represented with the planet Saturn or the Titan Cronus. This day is typically reserved for law, limitations, binding, holding, returning, blocking, stopping, collecting, changing, renewing, transforming and loss.
Moon phases also contribute, although this is more commonly used than symbolic days of the week. Like the moon, you build up and break down your work.
New Moons are like a fresh start or a clean slate. It's great for banishing, divination, curses, destructive magick, and soul searching.
Waxing Moons are times for building up or using creation magick. It's great for success, attraction, health, luck, friendship, and basically any goal you have in mind that you wish to work on.
Full Moons are great for just about any magick with love, charging, healing, banishing, cleansing, and clarity. This is a time most frequently used for one's highest potential and is not limited to anything.
Waning Moons are times for building down or undoing magick. It's great for undoing curses, undoing bindings, releasing negativity, cleansing, banishing, balancing oneself and atonement.
Hope this helps. Be sure to check out Raven's Gate!