Editing a Date time in dashboard

Is this a bug or am I doing it wrong. I have a hub variable that I only store the time in. I have a tile on a dashboard so I can edit the variable manually. The tile is fine as long as I change the value in RM, or on the hub variable page. If I try to manually change it in the dashboard I can not enter a time only. When you click the value in the dashboard you get a screen that shows a date and time. The only option to clear, clears both the date and time and closes the dialog. When you click it again it puts the date back, so you can't enter a time only.