I'm trying to work out which formula to use for summing values within a period of time and date. I have the following data:

I'm trying to work out which formula to use for summing values within a period of time and date. I have the following data:

I'm trying to work out which formula to use for summing values within a period of time and date. I have the following data:
A                B             C
 
 
Jan 1, 2011      8:00 AM       10
 
 
Jan 1, 2011      10:00 PM      15
 
 
jan 2, 2011      8:30 AM       20
 
 
Jan 2, 2011      9:00 AM       15
 
 
Jan 3, 2011      8:25 AM       11
 
 
Jan 3, 2011      9:00 PM       10
I need to add all values in column C which correspond to a certain date and time interval, say, Jan 1, 2011 9:00 AM to Jan 3, 9:00 AM. How can I do this?
 
Thanks & Regards
Dinesh