Your first two lines were frequently used in autograph books.

This is the oldest version I can find:

When the golden sun is setting
And your mind from care is free,
When of others you are thinking,
Will you sometimes think of me?

--from Charlotte Beckim's Autograph Album, 1892. (That site has an image of the handwritten verse.)

I also found numerous variations at other web sites:

1. When the golden [or "glorious"] sun is setting [or "sinking"],
[Or "When in the west the sun is setting"]

2. And your mind from care is free [or "set free"],
[Or "O'er the western sea,"]

3. When [or "While" or "And"] of others you are thinking,
[Or "When of absent ones you're thinking"]
[Or "When of loved ones you are thinking"]
[Or "And you are thinking of your loved ones,"]
[Or "When of over a thousand things you're thinking,"]
[Or "When of ten thousand things you're thinking,"]

4. Will [or "Won't" or "Do"] you sometimes [or "kindly"] think of me?
[Or "And then will you not remember me?"]
[Or "Will you remember me?"]

[1-4. Or "When the golden sun is setting
In the far and distant west,
While of others you are thinking,
Think of one who loves you best."]

I never found an instance where these lines seemed to be part of a longer poem.