before Abhilash & i could answer that question, you need to decide on what you actually want to display on the report.
if you limit the data via record selection filters, then that's a plus. i.e. if you eliminate any records that aren't involved in the wait time averages using a set of parameters to filter the data then you don't need to create a bunch of formulas to get you your end totals. if you need to have multiple sections on the report as per Abhilash's question above on what you want, then this of course is more work than creating an ad hoc style report where the end user filters and groups the report to limit the entire data set on the report to the required data set in the calcs.
for the time calcs, have a look at the attachment, changing the .txt extension to .rpt and take a look at the calcs at the right side of the report for an idea.