Clip duration in FCPX

One other thing: you may want to try converting these still images to a Quicktime movie before importing.

A single movie is far easier for FCP to handle than a thousand jpegs.

You can do that with Quicktime Player: File->Open Image Sequence, select the first file, and click Open. Then save the movie, and import that into FCP.

No, you don't have to adjust them individually.

1) Click on the first of the 1000 images in the event, then press Command-A to Select All,

2) press E to add to the timeline

3) In the timeline, press Command-A to Select All, then press Control-D, type the duration and press enter.

Done

I might also suggest doing this with Compressor if you have it, as it gives you more control or codecs and data rate and frame rates when you're converting the image sequence to video.