Final Cut Pro X: Change duration of an image not working

I'm trying to use ctrl D to change the duration of images (defaults to 10:00) in the timeline. My steps:

1. Select an image in the timeline
2. Press CTRL + D
3. Click on the purple time under the preview
4. type in 500 and hit enter

Result:

1. image stays at 10:00 length

I just can't figure out what I'm doing wrong

Using FCP 10.7.1 on a M2 Mac Mini