When you mouse over the end of the span, you'll see a double-sided arrow. Just drag when you see this and this lets you adjust its length. Hold Shift if you don't want your present keyframes to stretch along with the span. (This actually makes it way easier to adjust length than older tweens, especially if you want to stretch the tween).
You may want to check out this article for migration tips. http://www.adobe.com/devnet/flash/articles/motion_migration_guide.html New tweens work like span based selection has for a long time in Flash, but the article outlines some additional tips and tricks, with keyboard modifers and such.
Thanks for that tip jen. I think the OP is about how to move the diamond shaped property keyframes. At least that is what I took away from the question.
The trick is that you have to select them differently than you would a traditional keyframe. If you ctrl-click on the diamon property keyframe you can select just it. Then you release the ctrl and click again to drag it to a different frame. It is very non-obvious and I think I've had to learn it about three times and yet I still always forget it. I can't remember which order to do the ctrl-clicing in.
Thanks so much.
The control-click, release, click, move-- is what I finally figured out that worked for me.
Doesn't make much sense -- but at least I know how to do it now.
Sorry. I was keying into the "want it to be a few frames longer or shorter".
the article you posted was really helpful, regardless. Thank you.