A date

In "First To Thine Own Self" 12 February 1964, at the end a young cowboy named Randy sings a song about a young man who left Texas and went to Arizona, and gets a letter saying that his girlfriend married someone else.

And the song mentions Tombstone, a silver mining boom town in Arizona.

Army scout Al Sieber predicted that Ed Schieffelin would find only his tombstone while prospecting in dangerous regions. But in 1877 Ed Schieffelin filed for a mining claim he named Tombstone, and in 1879 the mining town of Tombstone was formed.

So the song that Randy sang was probably composed about 1880 to 1886 when Tombstone was a famous boom town.

So The Virginian episode "First To Thine Own Self" would have to happen after 1880 - if it happen in the real west instead of the Wild West of the movies and television.