Time stamped data

I have a table of data that has a time in column A and sales in column B.
I would like to analyse this data by weeks and time of day. eg Morning, Evening, etc. I can't get the daverage function to work with the time of day- it does fine with the date groupings.

Help!

A Date (same as Date_Time) is a floating point number
For example: 1/1/2007 12 PM is 39083.5
39083 days past the reference date, plus .5 days to represent 12 Noon (1/2 day past 12 AM on 1/1/2007)

To work with just the times of day, extract just the fractional part
.5 = mod(39083.5, 1)

Say the dates are in A. Extract the fractions (Times) in B.
You can use the usual statistical functions on the times, and they
will display as times when you format them as Dates or specifically as Time

But I couldn't get mod formula to work in a criteria range, so i just bit it and added some columns to the worksheet and let those do the work. YeeHaa, boy does that make a large spreadsheet!