right, as stated, i can see the video preview reflecting the edits.

my concern is about the timeline not showing a duration-change. maybe i'm dense, but if a clip is sped up, won't it then be shorter in duration?

Another comment.... I always go to 'switches' (right click on clip) and select "Disable Resample" for any velocity modified clips. This will prevent Vegas from trying to generate interpolated frames in your clip. "Smart Resample" always results in blurry, ugly frames and I don't see why one would ever want the frames interpolated when changing the velocity.

If one wants slomo, you need to shoot your video in a higher framerate than your intended playback speed. If one wants timelapse, then you just drop frames.

When changing velocity, the size of the clip does not change.... it just creates loops of it's self to fill the extra time (if you are increasing velocity). You should notice a little triangle at the top edge of the clip.... Just drag the right edge of the clip to the first triangle (further to the left) and you will have played the clip once at the higher velocity.

If you are slowing the speed down, then you'll need to drag the right edge of the clip further to the right (to the first triangle) in order to play the clip entirely.

If there is a way in Vegas to automatically resize the clip to one full loop of the clip when changing velocity, I don't know how. But that doesn't mean that there isn't a way. Maybe someone else knows.