how to make hourly average

I have data in excel file The first column is date with format 1/01/2005 1:00 until 1/01/10 0:00 including 366 days on leap year. The second column is gas demand in cubic meters. What I want to ask are: 1. How to make average for each hour for every for month? (x=00.00-23.00; y= gas demand; curve = jan-april, may-august, and sept-dec). 2. How to make average for each day on the week?(x=Monday, Tuesday, Wednesday, ... Sunday; y=gas demand). Any help is appreciated. Thank you