Quote Originally Posted by Alaskan
I believe the term daywear means casual and the term evening wear means formal.

So yes, the level of the formality of the occasion should dictate the sporran day or night. You shouldn't wear a fur silver mounted sporran if you are going to bars in your kilt at night, but you should wear it to a wedding (asssuming it is a formal wedding) that takes place in the morning.
Spot on, Alaskan!