No, I wasn’t trying for a House Rule: I have definitely seen the Latin 5 requirement somewhere… Possibly applied to some other task in the great mess that is The Rules.
My bad.
As to the Spell… Oy!
I have tried every which way to get the system to do this and it won’t. I agree that you should be able to create this spell as level 20 ritual and according to my understanding of the rules you should be able to do so in a single season. But…
First of all I tried the Design Spell dialogue (which worked fine for all the other spells you submitted):
This is the screen for when I had entered the spell:

And when I pressed Next I got:

With some tweaking I got the level of the spell down to 32 at this stage but I have no idea why it says the level is 20 in one dialogue and either 45 or 32 in the next.
So then I tried the Invent Spell dialogue which tries to do something similar but as if the character was trying to make the spell in the lab rather than having it at spell creation. Eventually I got this:

Why six seasons to invent it if it were only a level 20 spell?
I do not have a clue what is going wrong at this stage.
I need to be able to use the Metacreator to manage this campaign… But if I can’t get it to work I’m going to have to have Serious Thoughts.
Any suggestions gratefully received.