The first thought that came to mind was to set to "Normal" for the Time Zone of interest here.
But there is an easier way...in the top right corner of a Time Zone block is an X. Click on that to close and get rid of that particular Time Zone.
Please let us know if any of that works for you.
That did work, thanks. I didn't see the X because the time zone was totally collapsed (I had not pulled it to extend the duration from zero) and so there wasn't any X visible.
As I said, I could have left it there with normal speed, but my experience with many types of computer-generated items is that sooner or later this type of loose end can come back to bite you. At some point, some program won't be able to read that particular bit of code because it's zero change, or the duration is zero, or whatever. And you end up with a mysterious error message or other problem without having any idea of what the issue really is.
For example, I have found that if I have sharpened a clip in PE12, and then copied that attribute to all variants of that clip in the timeline, the sharpen setting is faithfully copied onto all the variants. But if I then decide it's too much or too little, and change the setting in the "mother" clip in the timeline, copying the new setting to all variants/clones as a group will not delete the original setting. Rather I'm left with two Sharpen settings in each of the "clone" clips: the original setting and the revised setting. Even though the "mother" clip in the timeline has only one setting, the most recent one. I couldn't figure out why the clones didn't look right, until I un-grouped them, and looked at one individually. Then I had to delete the extra Sharpen setting on each clone (a dozen in all) one at a time. Had I known this, I would have taken the step of removing the Sharpen from the "mother," copying this change to all clones, added the new Sharpen and copied this change to all. Who knew?