For many years Final Cut users have been asking Apple for an overlay layer that shows the timecode of clips at the play head. Chris Hocking of LateNite Films tweeted some evidence of some Apple experimentation:

@cailyoung @Alex4D Interestingly, enabling ‘Guards’ also enables timecode overlays, which is pretty handy! pic.twitter.com/ab02JbKkRj

— LateNite Films (@latenitefilms) August 13, 2015

You can only enable Guards in Final Cut by accessing the Debug preferences.

If you want to risk modifying your copy of Final Cut Pro X to make the hidden debug preferences visible, follow the instructions on Chris Hocking’s blog post, or watch my YouTube video showing how it’s done.