If the clips are still images they should all be the same length and you can
adjust that before dragging them to the timeline by clicking Tools > Options
[Advanced] tab and changing the picture duration. This operation will have
absolutely no effect on the images already on the timeline however so those
will either have to be adjusted manually one at a time by clicking and
dragging the right side of the clip or by removing them and dragging them to
the timeline again.
If you are talking about video clips that doesn't make much sense but you
can manually adjust the length the same way as images but you will be
cutting off the end of the clip.
-Wojo
