For anyone else curious about this - as I was - I have just worked out an easy way to do this. I have just finished a massive transcript and also wanted to highlight the timestamps, e.g. "The quick brown fox [0:04:10] lazy dog, but I only want the numbers highlighted. This is how I did it -
A simple Search and Replace:


Find: ^#:^#^#:^#^#
Replace with ^&
Format: Highlight



And then for extra efficiency, I've made it a macro to run at the end of of my document.