“Set creation time” is a new feature that was added to the latest version. It has to do with how the files are sorted in the playlist. It allows you to change the date the file you are using was created. You can do it in both the Playlist window by right clicking on a clip and also in the Properties window like you have there. Although I have noticed that the change only seems to stick when it’s done in the Playlist window and not the Properties window.
“Extract sub-clip” is an option to export a shorter clip from the original clip you have but without any re-encoding. You can select the specific section of the clip you want to export either by setting the in and out points in the preview window when you are playing the clip from the playlist then going to the Properties window or by choosing a clip in the timeline then going to the Properties window there. However, it still needs some work as some people have reported that it can be buggy: