summing by date

Hi have a list of dates and times with a number (hours worked) next to them, please see attached excel sheet.
I'd like to add the time per week, perhaps specified by the user.
Is this possible with functions or do I need a macro. I was thinking of a combination of sumif and the date function but I'm not sure if the date fuction will work with the date format I have in column A.

Thanks

Jon