No not all spells have to be casted on a Friday. They can be casted anytime or any day. It just sometimes, people believe certain days or times and different mooh phases help the spell become more stronger as it gives it more energy.
different days, even hours, are favoured by certain energies, so some people will cast certain spells on certain days, at certain times, during certain moon phases believing they would make their spell more powerful. if this is true or not, i don't know, but if you do believe this, research the lunar hours, the moon phase, and the aspects of each day to help you with your casting. if you do not believe this, then it can be cast whenever. so long as you charge enough energy, focus, and you actually need the spell, then it will work. [of course depending on the spell you might have put in some extra effort in your daily life for it to work, also if you're casting over someone their free will does play a part in the spell working.]