Earlier (antes)

[fglorca]

I called you earlier. (e.g. 8:00 this morning)
• Te llamé antes.

Is there another expression we could use here instead of antes?
I know más temprano is not correct here.

Many thanks in advance.

[aleCcowaN]

Not clear the context you have in mind. At least give one example for each context you want to have explained.

[AngelicaDeAlquezar]

@fglorca: You are right; "más temprano" doesn't work, since we'd need some usual hour to compare to, and that's not what your sentence is about.
Your sentence is fine, but it sounds a little fragmentary (¿antes de qué?). I might rather say "Ya te había llamado (antes)", where the conjugation makes clear that I had already made a previous call.

Also:
- Te llamé (temprano) en/por la mañana.
- Te llamé hace rato.

[fglorca]

How about:
Te llamé antes, pero no estabas en casa.
We could replace antes with hace un rato, couldn't we?

[aleCcowaN]

antes requires an event

[AngelicaDeAlquezar]

It's better with "hace (un) rato"; that is why I changed the verb in your previous one for "ya te había llamado", so there is a reference for using "antes".