Here we have a tutorial to customize button captions. So you can use {ENTITY STATE MINUTES:Status} tag to display wait time in minutes on buttons.
There is no built in feature to define time based button colors but it might be possible by using custom formatters (like <block> or <panel>) and some JScript code. We discussed something similar with kitchen displays to change duration font depending on waiting time but unfortunately that is not released as a tutorial as we replaced it task widgets.