I never thought about this until I read your comment and think I would have always chosen "morning, noon and night" as the correct version, but now that I've thought about it, I like "morning, noon, and night" better because I've found the other variant clumsy in certain situations. Sure, those situations are probably signs of badly constructed sentences (eg, nested lists or lists as an aside[1]), but still! The difference is that if I have a list "a,b and c" which is itself followed by a comma "(a,b and c),d" - to me, it looks like "a,(b and c),d" - but if there is a comma before the "and" it doesn't: "(a,b,and c), d" - the "and" now implies that c is the last item of the list, making the nesting obvious.

Just something that popped into my mind just now.

[1] Example: "I find lists which are followed by a comma, such as morning, noon and night, look awkward" vs "I find lists which are followed by a comma, such as morning, noon, and night, look awkward" - the first one reads as if "noon and night" is one item in the list, the second one as two (with night as the final item).