Can't convert hh:mm string to hour in field calculator

I have an original string field named "Hi" which I copied to an identical one Hi2 and then deleted (because I want the new one to be named "Hi").

The original "Hi" and "Hi2" are string fields that collect current hour with the following expression:

format_date(now(),('hh:mm'))

Although it works fine, I’d like to do the same but with a new date type field named "Hi" that includes the features of the previous field, but using

format_date(to_time("Hi2",'hh:mm'),'hh:mm')

returns a NULL value.

Sometimes the previsualization in the field calculator gives correct values (but the resulting field is empty) and sometimes returns de error

Can’t convert 11:17 to time]

How can I copy the original values to the new date type field?