It is very common to have to supply an output of your content with a Timecode overlay (commonly referred to as a Timecode Burn-In) for reasons such as:
Provide a visual Timecode reference (or other data, for example, film edgecode) for a visual effects artist, music composer, sound designer, sound mixer, or film negative conformer
To indicate the version and/or date of the output, who is receiving the output, and/or to place a copyright notice
For this recipe, we'll be using the relatively new Timecode Burn-In effect found in the Generator category of the Effects Palette. Not only does it play in Real Time (and if rendering is required, it will render much faster than a Non-Real Time effect), but it has multiple displays and a great deal of customizability.