@kellyms , greetings! As far as I'm aware, you can't edit the timing of videos in Studio (Arc) directly, just the word content. To change the video timing, I'm guessing you'd need to create an SRT or VTT file with the captions (and timings) and then upload that to Studio - https://community.canvaslms.com/docs/DOC-9664-50736657092
Hello @kellyms ...
To add to what @kona said, you can download the SRT or VTT file that Studio (formerly called Arc) generated for you, and then you'll need to open up that file in something like Windows Notepad (or whatever the equivalent would be on a Mac). When opening the file, you'll probably need to select "All Files" because Notepad doesn't usually open those kinds of files. Once the file is open, you'll see something that looks similar to the example shown on this site: https://www.3playmedia.com/2017/03/08/create-srt-file/. You'll be able to change the times of the captions...along with the text. Just be aware that if your video is quite long, this is going to be a long process for you. Then, upload the file back to Studio.
Hope this helps, Kelly.
An alternative for you: upload the video to youtube edit the subtitles there, then download the youtube subtitle and upload it to ARC.