Say we have data in cols A & B like:
Thursday, January 01, 2009 06:45
Friday, January 02, 2009 05:01
Saturday, January 03, 2009 01:07
Sunday, January 04, 2009 00:52
Monday, January 05, 2009 04:44
Tuesday, January 06, 2009 00:44
Wednesday, January 07, 2009 05:36
Thursday, January 08, 2009 01:23
Friday, January 09, 2009 01:43
Saturday, January 10, 2009 03:28
Sunday, January 11, 2009 01:31
Monday, January 12, 2009 00:50
Tuesday, January 13, 2009 03:07
Wednesday, January 14, 2009 00:46
Thursday, January 15, 2009 02:04
Friday, January 16, 2009 02:11
Saturday, January 17, 2009 04:34
Sunday, January 18, 2009 02:55
Monday, January 19, 2009 03:38
Tuesday, January 20, 2009 04:34
Wednesday, January 21, 2009 04:45
Thursday, January 22, 2009 01:03
Friday, January 23, 2009 07:03
Saturday, January 24, 2009 06:24
Sunday, January 25, 2009 07:11
Monday, January 26, 2009 04:03
Tuesday, January 27, 2009 06:57
Wednesday, January 28, 2009 04:01
Thursday, January 29, 2009 04:05
Friday, January 30, 2009 06:22
Saturday, January 31, 2009 06:09
In C1 enter:
=WEEKNUM(A1) and copy down
In D1 enter:
=SUMPRODUCT((B$1:B$365)*(C$1:C$365=ROW())) and copy down thru D52
Correctly formatted column D will give the weekly sums:
12:54
18:35
15:07
06:24
14:52
11:48
17:20
08:17
23:16
02:23
20:32
22:14