When I change the field in the data edito to time only, I get this:
In the Google sheet it is this:
In the app it is this:
I think you might need to have a complete date in MM/DD/YYYY HH:MM. The date probably doesn’t really matter, as long as its valid. Could probably use 01/01/2020.
The odd thing is I tried to do the same thing and I didn’t get any time to show up at all. Maybe it’s something to do with me using 12 hr time instead of 24 hr time. The data editor and the data in the app showed a blank time, but it seemed to work when I added the date in addition to the time in my sheet.
I still formatted the column in glide to only show time, but it appeared to work.
Could @Mark say something about this? It would be a nuisance to have to fill in MM/DD/YYYY HH:MM when you only need HH:MM 
Could you share the app, please?