I'm not a mother tongue speaker but I'm pretty sure that the correct form is 'two weeks' notice', genitive of measure. If, as I believe, in this case 'notice' is countable a possible alternative is 'a two week notice' like 'a three day ticket' or 'a stone merchant' but the form in the title of the film doesn't make sense because it would be a compound with the first part -grammatically an adjective- treated as a noun: consider the difference between a twenty-year-old boy and a twenty years old.