You can cast your spells whenever you want, without following and listening to what astrology teaches you about proper planetary hours and days for casting any category of spells.
Casting your spells according to planetary hours and days is only optional, so your spells will work just as it does in recommended days if you know how to cast it and perform it.
Just like moon phases, tools and ritual supplies, chanting and circles, casting your spells according to specific planetary hours and days is only optional , so you can do what you will. It means that everything will be fine if you do not follow this optional step. You have many options in magic, many of them are not necessary at all, just as following astrological /planetary days or hours and all of the other optional list of criterions I've listed here.
Planetary hours and days basically serve a symbolic value which comes from astrology and focuses on different things symbolically, which you choose if to follow or not.
What you do need to necessarily follow while casting your spell is raising and building up energy, directing it for a specific intent / desire, which is basically the idea of spell casting and how it generally works, without any optional additions and steps ( which are helpful by the way).
Do what you will in your spells and follow whatever steps you wish to follow. Just remember how spells work and how you're doing it.