Add hours next to a given date

Hi
I have a spreadsheet where I have dates and next to them hours for a given day.

I want to add the hours total for a date - which I have done manually. Is it possible to have a function on col C, which adds the hours from a given date until another date. There can be different number of rows below a given date as can be seen on the spreadsheet.

Thanks in advance for your help.

at C2 (array formula )
IF(A2="","",SUM(OFFSET(B2,,,IFERROR(SMALL(IF(LEN($A$2:$A$24),ROW($A$2:$A$24)),COUNTA($A$2:A2)+1)-SMALL(IF(LEN($A$2:$A$24),ROW($A$2:$A$24)),COUNTA($A$2:A2)),100))))

copy down

Thanks Ghozi Alkatiri.

Exactly what i wanted.

Cell C2 array formula , drag down

HTML Code: