Impressively enough, Nova not only doesn't have a Time field but also doesn't support a time-only usage of DateTime field.
On the other side, Nova has plenty of third parties componentes that can be easily added via composer. I did look for some on Nova Packages and found two viable options: Laraning Time Field and Michielfb Time Field, they seem to be pretty good and open-source.
Nonetheless, they have relatively few stars on GitHub and a rather old latest version, which is not much of a problem for such a simples functionality, but I'd rather go with a native one, so here is how I implemented it:
Text::make('Duration')
->placeholder('##:##:##')
->rules('date_format:"H:i:s"')
->help('hh:mm:ss'),
So basically I used the Text field with a format validation. Also added the placeholder and help attributes to make it a bit more intuitive. It works well! and I'm using it with a time
database field. Other colleges suggested using a masked component but it would also require a third party one and I didn't find a good option.