The word "except" is used here to show an exclusion and links the noun "Friday" to the rest of the sentence. Therefore, it functions as a preposition.

১. When "except" means "but" or "excluding", it is typically a preposition.
২. It cannot be a noun as it doesn't name a person or thing.
৩. It doesn't modify a noun like an adjective would.

অতিরিক্ত তথ্য: "Except" can also function as a verb, meaning to exclude.