later or until later or not until later

Question

Today I saw this phrase "until later" and am almost confused now.

A person says "I'm supposed to start on a new department, but not until later today"

In this context, "not until later date" indicates "after date" I think.

Then I'm wondering. How do you make a choice among later, until later and not until later?

ex:I want to buy this but (later/until later/not until later)

I can't tell which sound natural and which sound weird.

Answer 1

"Not until later" is generally preferred over "later" in clauses that are contrastive. Since your example sentence at the end has a clause starting with but, you're introducing contrast and so should use "not until later."

Your first sentence could alternatively be phrased, "I'm supposed to start on a new department later today." But by changing the last part to a contrastive clause, the speaker is emphasizing that there is a period of time before they will actually start.

"Until later", without not, is not contrastive. It simply specifies a period of time when some action will stop or change. For example, "I'm waiting until later to talk to her" says that I'm currently waiting, but at some point soon I will stop waiting and talk to her.

Answer 2

I may not be surely correct but I will use these three words here differently which I hope will clear the concept.

1. I want to buy this later.
2. I don't want to buy this until later.
3. I want to buy this but not until later.

To me this is it. But anyone who wants to change this?