1. I want the new closed caption duration to have the same duration as my video.
I am finding it impossible to logically extend it in the timeline.
In my timeline see attached it jams at approx 27 seconds and says trim media limit reached?
2. When I select new item and create a new closed caption stream it is created in 2:22 blocks.
Can't I select a duration?
The Out timecode of the last caption block defines the duration of the caption asset/track item. So if you add a caption block in the Captions panel and set its Out time to the desired value, say 00;00;35;00, then you'll be able to trim the track item out to that point.