Formula giving wrong total duration between two dates

Dear Sir, Madam

Please find attached file, I am trying to calculate total duration in Hours between two dates, I use custom field HH:MM and formula Actual Finish - Reported Date.

But why giving wrong output ?

Regards;

Dear Alan,

Thank you for your e-mail, I checked but if the date is within two different dates instead of the same date it will give wrong output.

Regards;