Pivot table sub totals

[eli]

Hello everyone,

here is my question (thanks in advance for your feedback)

I have data entered in columns in excel. First column is
dates, second one is events, 3rd one is the time per
event. Each sheet on my excel spreadsheet is a month.
I have multiple entries per day. looks something like
this:

28 July address 10
28 July bank 5
29 July change 15
etc....

The list of events is drawn from a validation list, the
list has 8 events.

I have created a pivot table, i get the sum, average and
count calculated on a daily basis and i also have the
grand total at both ends (bottom and far right)

I would like to know is there a way that i can have
sbutotals inserted on a weekly basis in my pivot table
once all my data is entered at the end of the month ?

What is the easiest way ?
Can this be done ?

Thanks