>
> I would like the following result.
>
> 01:00 + 03:30 + 01:45 = 06:15
>
> would return only the sum
>
> no matter whether it is morning or evening, this field saves time
> allotted and not hours
>

As others have pointed out, you can not sum time columns. But you can extract hours and minutes from the time value and sum that like this:

select 60 * sum(extract(hour from t_col)) + sum(extract(minute from t_col)) minutes
from times_table

However, if you are storing durations in time column, you should actually use integer or double for that.

Sasha