I nearly drove myself silly trying to do the same thing. It ought to be easy, but it isn't.
In the end, I added some columns, over on the far right hand side of the spreadsheet. They are 30 days, 60 days, etc, and follow the general principle =IF(A3>(TODAY()-30),B3,0)
Column A is date, Column B is hours and decimal.
Then I just add the relevant columns. The totals copy over to the "summary" detail bit of the logbook.
It's ugly, and inelegant, and it works.