Learn English – How to say any day after a particular date

Normally you would say:

I will come back to you later.

if you are staying on the connection (internet or phone).

If you will drop the connection to resume later on, then:

I will get back to you later.

This also works in personal communication. Let's say you ask your professor something, but he needs to speak to another student first. He might say to you:

I will come back to you later.

When he does, let's say he needs to do some research back at his office before he can answer. In that case:

I will get back to you later.

Some people might use "later on", but it is unnecessary.

Short answer: no, not really. You're looking for a word like anteayer in Spanish? We don't really have anything exactly like that. We used to have "ereyesterday" (and "overmorrow" for the day after tomorrow) but they are archaic now, and people will not understand those words if you use them. "The day before yesterday" or "day before last" are the common ways to say it.

There's a discussion of the topic at English.stackexchange.com here.