No, you have to do it on the clip. What's confusing about it? Just zoom in close, set your points, stretch as needed, move the bar to the percentage you want it to be and match the other clips to that.
Or... you can put them all in a nested sequence and apply time effects on that
Or.... you can render them all out at original quality, bring them back in and modify that clip as one clip.
I've nested my 3 tracks. I am able to apply time mapping. I'm editing one for reference, and when all speed has been fixed, I'll paste those edits onto the other two tracks.
Here's my next concern: I do not have all my assets yet. I have all the reference footage needed for editing, but there is alot more media coming, not yet ready, (hence the other 2 tracks) that will sync perfectly with my reference. I had the foresight to lay "dummy" files in place of the presently incomplete assets. My plan was to do a "footage replace" after the fact. Complete the assets and swap them in.
Big question is, after all my time warping is done, and I've copied the warping to the other 2 nests... what happens when I open up the nests? Will all the warping info be transferred to the content that had been nested?
That would be ideal. Then I could swap in the completed media.