Change duration of still frames in iMovie 10.0.7 I am making a video that contains both video footage and still frames but I can't find where to change duration of still frames to longer than 4 seconds.

How can I change the duration of a still frame to be longer than 4 seconds in iMovie 10.0.7?
Open the app and search for Freeze Frame in the help menu.

Select the help topic named:

- Add a freeze frame

It explains how to freeze a frame and at the bottom of the page, it describes how to modify the 4 second default.