Big-time and High up

Big-time adverb - To a large extent or degree.

High up and big-time are semantically related In some cases you can replace phrase "High up" with "Big-time", this phrases are similar.

High up adverb - At a great altitude.

Big-time and high up are semantically related in eminent topic. Sometimes you can use "Big-time" instead an adjective phrase "High up", if it concerns topics such as important.