Slideshow of video clips/timestamps?
Solution 1:
Unless you have a fairly old version of PPT, you can tell it what portions of a video clip to play.
Select the video, choose the Playback tab on the ribbon, then click "Trim video". From there it's pretty much intuitive.
If you're going to use the same video several times, insert it once then copy/paste it wherever else it's needed. If you do that, PPT will retain only one copy of the video rather than a copy of it for each slide.
The file will grow, possibly even considerably, when you do this because PPT will also generate a "poster frame" image for each instance of the video. If space is at a premium, you could replace the poster image with a smaller one.
On the Video Format tab for the selected video, choose Poster Frame and pick another image. You could even use a screen capture of the image of the video currently displayed on screen and saved as JPG ... in some cases PPT saves the poster frames as PNG. MUCH bigger than the equivalent JPG.
[Later, after a few tests] Even simpler than I thought: Rightclick an inserted video, choose to Save As Picture and save it as a JPG. Then select the just-saved JPG as the poster frame for the video. Result (at least in this particular case): An embedded 65k JPG image replaces a 2+megabyte PNG for each video you do this to. Use the same JPG for each video and you eliminate substantial tonnage. In my test case, doing this reduced a 12+MB file to 4+MB (of which most of the 4MB was the video itself).