As paweld says, it must be a integer or real value stored in the database. ilość godzin mean sum of hours is google translate is right.
If you store hours (as int) and part of hours (real, float) it is not compatible with datatype Time nor with DateTime. You have to convert this explicit to get TDateTime or Time values.
And to store numeric values in string is not a good idea, becaus you cannot work with a lot of built in functions of the Database server.