You mean the timeindex for the clip for the vod/.stream that is was clipped from? So for example you can go back to the vod and capture stuff before/after the clip?
You can take the clip slug that you got from Helix, and perform get clip against kraken
That has the information you are after.
https://api.twitch.tv/helix/clips?id=MushyVenomousSnakeOpieOP
compared to
https://api.twitch.tv/kraken/clips/MushyVenomousSnakeOpieOP
Kraken/v5 just has more of the needed data