What comes to mind is:

Taurus (the constellation)

The "cow" reference is pretty obvious. It also fits in with the title hint

(horoscope)

and the "group of siblings" might be referring to

Pleiades/Hyades.

You might see it only at a certain time - "if it's your time", i.e.

if you're, for example, in the Northern hemisphere's winter or spring... although 6 a.m. seems to be a bit too late.

Edit:

I believe it's not the entire constellation, rather a group of stars (as Ivo noted in the comments) - either the Pleiades or the Hyades, since in Greek mythology, they are the children of Atlas, a titan condemned to hold up the sky.

What comes to mind is:

Taurus (the constellation)

The "cow" reference is pretty obvious. It also fits in with the title hint

(horoscope)

and the "group of siblings" might be referring to

Pleiades/Hyades.

You might see it only at a certain time - "if it's your time", i.e.

if you're, for example, in the Northern hemisphere's winter or spring... although 6 a.m. seems to be a bit too late.

Edit:

I believe it's not the entire constellation, rather a group of stars (as Ivo noted in the comments) - either the Pleiades or the Hyades, since in Greek mythology, they are the children of Atlas, a titan condemned to hold up the sky ("Some say my predecessor can hold up the world").

What comes to mind is:

Taurus (the constellation)

The "cow" reference is pretty obvious. It also fits in with the title hint

(horoscope)

and the "group of siblings" might be referring to

Pleiades/Hyades.

You might see it only at a certain time - "if it's your time", i.e.

if you're, for example, in the Northern hemisphere's winter or spring... although 6 a.m. seems to be a bit too late.

What comes to mind is:

Taurus (the constellation)

The "cow" reference is pretty obvious. It also fits in with the title hint

(horoscope)

and the "group of siblings" might be referring to

Pleiades/Hyades.

You might see it only at a certain time - "if it's your time", i.e.

if you're, for example, in the Northern hemisphere's winter or spring... although 6 a.m. seems to be a bit too late.

Edit:

I believe it's not the entire constellation, rather a group of stars (as Ivo noted in the comments) - either the Pleiades or the Hyades, since in Greek mythology, they are the children of Atlas, a titan condemned to hold up the sky.