5:12 technically it is possible to change the thumbnail, but it is currently not in the d.tube interface. It may be done programmatically (which can be difficult) or using the thumbnail swap tool in my 3rd party uploader that I developed myself as part of the OneLoveIPFS hosting services run by @onelovedtube.

If I have the time I might fix the edit section in a pull request and include a thumbnail swap tool in there.