@tom_abramov,
You have a solution from @ms response. However, we either have very different JMP versions or we were not communicating very well, so this is an FYI response.
Your screenshot showed nominal modeling but only displayed time, 08:49:46 PM. If this column was numeric, not character then Informat() will return an empty because it's argument needs to be a string/character. So, it is important to specify whether your data is numeric or character, and or attach a sample data table.
If your incoming column is a DateTime column just formatted as time and it is numeric, I suggest you create a new column using the function/formula Time of Day(column 1) then format that new column as Duration. Even when a column is formatted as just time, if I wanted to find the time between say row 1 and row 2 and of the DateTime column just formatted as time it would include teh number of days, the underlying data is still datetime.
From the Main Menu, select Help > Scripting Index > Functions > Date Time there are example scripts you can run to see how each function works, whether its argument is string or numeric. This is an easy way to learn more. FYI