What is the difference between "I enjoy not working late" and "I don't enjoy working late"

What is the difference between "I enjoy not working late" and "I don't enjoy working late"?

By the way, if they mean the same, is one more common in US than UK?

I enjoy not working late.

This means that you like it when you leave work on time (or early).

I don't enjoy working late.

This means that you don't like it when you do work late.

The first emphasizes something that causes enjoyment, while the second emphasizes something that causes the lack of enjoyment. In other words, the former is positive, while the latter is negative. It could be looked at as a half glass full or glass half empty interpretation. In short, somebody who says the former could be thought of as an optimist, while somebody who says the latter could be thought of as a pessimist.

Also note that neither explicitly necessitates its opposite.

The following expansions are possible:

I enjoy not working late. (I enjoy working late too, but in a different way.)
I don't enjoy working late. (I actually don't enjoy working at all.)

However, we generally do assume the opposite to apply unless explicitly stated otherwise:

I enjoy not working late. (But working late is a pain.)
I don't enjoy working late. (But leaving early is great.)