I did a blog post on this topic a few years ago. You can real the whole post here, but here's a summary of my thoughts concerning the appropriateness of tartan hose during the day.

Fashions obviously have changed over time. Back when cadadh were the only hose worn, they were almost universally tartan, and worn day and night, formal and casual. When knit hose became more popular, so did solid colors. Knitting in a tartan pattern (Argyle hose) is obviously harder than knitting in one color, so tartan hose became less common. Though people still made the effort to acquire and wear tartan hose, more than likely due to the enduring popularity of the look of the cadadh.

By the time we get to 1901, Erskine (author of The Kilt and How to Wear It) says that tartan hose are for evening wear, except for "livery servants, pipers, or day fulll dress."

Fast forward to 1979 and Thompson (So You're Going to Wear the Kilt) says tartan hose are "for evening only" with no exceptions!

Jump again to 2001 and Martin (All About Your Kilt) reminds us, "The books say
that 'tartan' hose should not be worn during the daytime, without remembering that kilt hose were originally of tartan cloth, cut from the piece and worn all the time (cadadh)."

In other words, he sees no inherant reason why one couldn't wear tartan hose during the day. Nor do I.

I think one reason why tartan hose are most often seen for evening wear is that they do look fancier and are unquestionably the preferred hose for formal dress. That is not at issue here. The question is should they be worn only for formal evening wear.

Another factor that has been mentioned is cost. They generally do not come cheap, and most people will understandably reserve an expensive item like that for special occasions, meaning they will tend to use them only for formal dress.

But is any of this a reason to tell people they should not wear their tartan hose during the day? Not to my mind. While I can easily imagine casual day outfits where tartan hose would look horrible, I have also seen some people wear tartan hose during the day with much style and panache. I think they certainly can look nice with "day full dress" as Erskine described it.