How to display timecodes with iMovie 10.0.7 N

On discussion forums, I read that I have to go to iMovie Preferences and ask to display timecodes.

http://ift.tt/1BihZRs

But my preferences window only contains two checkboxes, none of them related to timecodes.

Do you know how to see the timecode for a given image in a movie ?

Thanks for your help !