Spaulding,
I have devised a logbook spreadsheet for my own use. It has some time calc in it that takes a time entered as a normal decimal (1.50 for one hour fifty mins) and converts it all to minutes, tot's it up and displays a running total in the column header in the format xxxxhxx (ie, 125h35)
There are no bells and whistles, and it hasn't had a great deal of testing as yet, but it gives you a vague idea how to do the time calc.
PM me if you would like a copy and I'll gladly email it to you.