"Everyday" is not interchangeable with "every day".

[Trills]

It's a very minor point.

It's unlikely that anyone will ever be confused about the meaning of the sentence.

It still annoys me that the loos in our office have a sign saying "Toilets are cleaned everyday".

How annoying. The standard or English is dismal in this country - I would tippex it out!

It's easy to add an apostrophe with a marker pen (or remove one with tippex) but how does a guerilla pedant add a space between two letters?

I would also be inclined to take a pen and correct the sign. But at least there is no rogue apostrophe - my pet hate.

Suppose at least it isn't "Toilet's are cleaned everyday"....