Datetime variables, please point me in the right direction

I see that there are datetime time variables and I use them to trigger actions at particular time of day (not interested in the date part).

When I created a datetime variable to be used in this way, I just don't fill in the date and click the box.

Is there a pure time variable?

What should I do about the date?

I have had problems when I change the time in a non Hubitat dashboard of "bad date" being reported in RM.

Thanks