Example:
After a joyous and restful three days, I left this beautiful city.
Although it still kind of sounds weird to my ears, I know that when a noun, even though in the plural, is used to mean a certain amount or quantity of something, grammatically there should be an indefinite article placed in front of it. But, can you think of a rule that I could utilize to tell whether I actually need one? Because I don't see anything wrong with saying after joyous and restful three days, I left this beautiful city. DoesWith that change, does the sentence now sound wrong to you?