I try to work with the lunar phases as much as I can, but do the days of the week really matter that much? For example, I know that prosperity spells are best done on Thursdays and protection/banishing spells are best done on Saturdays. But what if for some reason, I couldn’t do those specific spells on those specific days, would it have any negative effect on the result of the spell if I do it on a different day?
Thank you 
Do it now while the moons close to still being as close to full. Do it while there’s still time. Lol
Good question.
I’m not sure. My opinion is that it might just not be as powerful in potential as it could be at a time where planets and the moon are aligned a particular way which affects the “quantum” world/energy waves.
Tem
Try it out, see if it works for you, that’s the best way to gauge.
I’m kinda in the same boat with you, been following the Lunar cycles, and now about a year into my practice, as I’m progressing (I hope 
), looking into days of the week as well. So now we are in the Waning Gibbons, including yesterday, so Saturday would have been the day to perform the protection/banishing spells. There is also Tuesday coming up, ruled by Ares (and other deities as well) representing battle and glory, can use that for banishing/justice type spells, Then for the rest of the days during the waning, like Thursday for prosperity, or Friday for love and beauty, can light a candle representing such, just to keep the energy from the Waxing phase flowing through the Waning, but of course don’t perform those types of spells during the Waning, if following the moon cycles.
It sounds like a good idea following the days as well, compartmentalize and localize the energies, establish more of an order, control the ebb and flow more? Again, try it out! In this wonder world of magic, won’t truly know or feel it until one does it. 
I think you could cast those spells on any day of the week without negative consequence. I am a big fan of correspondences but that is just my personality. If I can put something in a chart, I will If you have a need to do a spell on a particular day, that need would be tied to intention, emotion and action, and those are big parts of spells, as well as your belief it will work.
One idea would be to use the herbs or tools associated with that day of the week. For example, many herbs associated with Mondays are protective. You could do some mirror work for your Monday protective spell.
Or you could let the correspondence help shape the flavor of the spell. A Tuesday prosperity spell might be about fast money to pay a debt, a Wednesday one about a business deal or lottery ticket, a Saturday one might be about savings. You might cast a protective spell on Thursday for a pet or the home or Friday for a friend.
While I try to work with the correspondences, I also use planetary alignments. When Saturn went direct, it wasn’t a Saturday but I did Saturn invocations and spellwork. Same for Jupiter. I think the Spells8 lunar spells are set up the same way – if the moon is in an astrological sign, it aligns with those correspondences. The more I learn about the correspondences and deities associated with them, the more meaningful they become for me, though. Those connections enhance my personal practice.
Depending on the spell, I try to cast it on the best day of the week, but sometimes that’s not always possible, so when that happens, I just do it as close as possible to the best day.
I think the day is only important if you want it to be. I’m not going to wait for a Thursday to do a money spell if I’m in a pinch for cash, for example. They can add power and correspondences to your work but they won’t not work if you don’t use them.
Thank you all!! I did a couple in the past that were on the “wrong” day and they seemed to work. I just wanted to check and see what other people’s experiences were like. Also, to be honest, before becoming a member here, I didn’t really understand much about lunar phases either, but I am learning as I am practicing and it’s just been a fun ride so far Thanks again for your input and have a great Monday 