How to group data by 5min instead of hour/1min

In my excel file i have the following:

Row Labels.............|......Sum of Count

ALICE...................................2751
9/28/2012 11:42.....................833
9/28/2012 11:43.......................84
9/28/2012 12:07.....................917
9/28/2012 19:34.....................138
9/28/2012 19:35.....................779
ALI..........................................78
9/28/2012 16:37.......................78
BELLA...................................2429
9/7/2012 11:34.......................230
9/7/2012 11:35.......................984
9/7/2012 11:38.........................56
9/7/2012 11:39......................1159

If i do a left click at any timestamp to group by hour, Excel will group by hour, then sum up the values.
What can i do to indicate to group by 5 min instead of 1min?
For e.g:

Row Labels.............|......Sum of Count
ALICE.............................2751
9/28/2012 11:42.............
.....................................917
9/28/2012 11:43............
9/28/2012 12:07.............917
9/28/2012 19:34.............
.....................................917
9/28/2012 19:35.............

So for Alice, it is sumed up into 3 groups.
As for Ali, it shall remain as the same: 9/28/2012 16:37.......................78 (there is no other records within 5min etc)