Hello,
If I am not mistaken, you cannot assign a column with a Time format to a slider. You can assign a Time column to any other type of control (drop-down list might be the best alternative.) I am checking with the dev team to verify whether that is correct.
In the latest release of VA, I can assign a time parameter (really a datetime parameter with a Time format on it) to a drop-down list control and it seems to function as intended.
Sam