I have found it to be true that each day is ruled by a planet and those influences can help us in the power of our spells if they are called upon on a certain day in a certain way. It is not absolutely necessary to do the spell on that day however we may lose some of the influence of that planet in our spell workings when it is not performed on that day. That is why some spells indicate that it should be cast on a certain day. The newer we are to magic is when we should follow the instructions for each spell as much as possible and even more precisely because we are still learning and do not always have all the information we need to exclude peaces of it.
I am new to the day planet influences. My information indicates that Friday is ruled be Venus which influences family, love, relationships, etc.... Its a huge list that includes gardening and creative type activities too Thursday according to my information is ruled by Jupiter which influences business, logic, gambling etc... another huge list.
If you email me I will give you more specific information or the link to get a pdf of what I have through the same store that I got mine through. It includes information on days, planets, the moon and sabbats. Inexpensive but not free. So for the information has been very useful.
I have mailed you with an in-depth explaination of exactly what I meant by my post. I did this to keep the forum more on topic. If you are interested in what I have to say, please look at the upper right corner of your page and chack your mail.
The spell in question, is likely referring to planetary days/hours. Friday is the day of Venus, and is "most" suitable for all operations that fall under the domain of it's planetary ruler. In this case, operations involving beauty, lust, love, passion, or any other operation attributable to Venus. That's not to say that other operations won't work on Friday, or that operations that are Venereal in nature will not work on other days, however.....
Knowledge of planetary days, hours, moon phases, etc is a fundamental part of effective magick. Although it is not necessary to abide by them entirely, it's foolish to think that going against the grain is the best way to achieve any truly effective work. You can add a drop in the bucket and hope for the best, or you can learn to use the current to add true momentum to your workings.
Spiritual energies are cyclical, like a massive unifying current that influences everything on some level. The best practitioners, are those who learn to work with the current, rather than trying to go against it. This is the very heart of occult learning.
The most important part of any spell is the belief and mindset of the person performing it. Some prefer pomp and ceremony, always following correspondent aspects, every single time. Others are content (and absolutely successful) whispering an incantation of their own design into the wind. Both are absolutely correct, so long as they feel so to the person practicing. There is no absolute way, one single way that separates proper and improper casting. None whatsoever. That's what sets us (most of us) apart from the other more strict religions in this world. We are the ones who walk in harmony with Nature, and as such should do what feels Natural to us individually.
Let's not start fights or belittle the questions of others. We know how important it is to keep asking to keep growing. Making them feel bad for asking only discourages asking more in the future!
To answer the original question: look into the more traditional meaning a of days, times, moon phases that can relate to spells and decide what feels right to you. If you want to apply those principles to your craft you feel free to do so. If you want to add something, do it! If you want to use another day becaus it seems more relevant to you, that's the most important part!
Those details only lend you energy if you need them to. The real energy is from you!!! Keep reading, keep practicing, and more importantly- keep asking questions :)