You can have iMovie display the precise duration of the video clips in your Events (source video), and of the video clips and other elements in your projects. iMovie displays this timecode information in the standard format of HH:MM:SS:Frames (hours, minutes, seconds, frames).
To display timecode values:
Choose iMovie > Preferences, click General, and then select “Display time as HH:MM:SS:Frames.”
The iMovie menu appears in a light gray bar across the top of your computer screen.
In the Project browser, durations are displayed in timecode format as you move your pointer over the left end of video clips and over transition effect icons. They also appear in the upper-left corner of the colored bars that represent background music, titles, sound effects, and voiceovers.
In the Event browser, durations are displayed in timecode format as you move your pointer over video clips.
You can also set iMovie to show playhead information, which lets you see the timecode values for the frame where your pointer rests as you skim your video.