Here’s a very simple mod called OmniCC, short for Omni Cooldown Count.

It will simply show numerical cooldowns in any slot that uses the default models for cooldown counts (i.e. most things).

Very simple to install and requires almost no configuration. The only thing I do after installing it and starting WoW is write

/omnicc mmss

in the chat window. That will change OmniCC’s output to minutes and seconds instead of just minutes for cooldowns shorter than 3 minutes. So, for example, a 1 minute 29 second cooldown will be displayed as "1:29" instead of "1 m"