Aggregate the time data (mm/dd/yyyy:hh:mm:ss) into the 3 hours range
 

Hi, I need to aggregate the time data (mm/dd/yyyy:hh:mm:ss) into the hourly range.

So, basically if I have 10 observation 7 days, I want to put them into the 3 hours range window and see that how many observations I get on 3 hours basis. Example is given below. Thank you very much in advance.

09/08/2013:23:46:41 09/08/2013:03:00:00
09/08/2013:23:50:19 09/08/2013:06:00:00
09/08/2013:23:50:46 09/08/2013:09:00:00
09/09/2013:00:27:04 09/08/2013:12:00:00
09/09/2013:00:45:20 09/08/2013:15:00:00
09/09/2013:00:45:21 09/08/2013:18:00:00
09/09/2013:00:45:21 09/08/2013:21:00:00
09/09/2013:00:45:21 09/08/2013:24:00:00
09/09/2013:00:45:21 09/09/2013:03:00:00
09/09/2013:00:45:21 09/09/2013:06:00:00
09/09/2013:00:45:21
09/09/2013:00:45:21
09/09/2013:00:45:21
09/09/2013:00:45:21
09/09/2013:00:45:21
09/09/2013:00:45:21