Not that I know. Edits are just entries in a list. The time of the last entry is known (and can be found with a smart collection), but not every single entry separately. Just curious: why is it important to know the time you made a certain edit?
I would like to keep track of when I did which work. For my time sheet and for the calculation of the effort. Since the timestamp is available for import/export, I could imagine that it is stored internally in the LR database with every command and maybe it is just not displayed in the frontend...
Say you go back to a photo that you edited 5 years ago. You start making additional edits to it now because since 5 years ago your editing techniques has changed and new Lightroom features give you additional control that maybe you did not have before.
You get carried away with some changes and now you realize you want to compare with how it was before or maybe you don't like the new changes and want to revert back to how it was before. With a timestamp, it would be easy to see which are the recent edits and which are the old ones. Without a timestamp, you'd need to remember the first edit you made and find it in the history list.
Yes, snapshots can be used to save the state of the picture before you start making edits, but that would imply that you remember to create the snapshot. I don't think you have to live with the fear that you forgot to take a snapshot, not when LR already stores the timestamp internally and could be made available easily as hover info.
If anything, the snapshot creation could be further enhanced or automated with a user option that allows the user to specify after which interval of time an automatic snapshot should be created before further edits are allowed. So if I have an edited photo that I haven't touched in 2 years and i attempt to make edits to it, I could be prompted to make a snapshot for it before the edits are applied. This mechanism already exists in LR when it comes to softproof copies. When you attempt to make an edit to an image in Softproof mode, you are prompted to first create a virtual copy if the image is not yet a virtual copy.
I am sure there are many other applications for which you would need to see the timestamp of an edit, but that's just one I came across just recently myself.