I pulled all of my data, put it in a spreadsheet, then sorted based on departure date. Figuring out how to add all the flight time was a little tricky, but used a couple of extra columns to separate out the hours & minutes (=HOUR(<time column>); =MINUTE(<time column>)), summed the hours, then summed the minutes and divided by 60, then added the two for the grand total.

I hope this is all an exercise in getting smart on Excel and nothing more...