I had a quick look at an old logbook. In my (albeit short) time on 56(F) in the early 1980s, my average monthly total, with no allowance for Christmas, annual leave etc was 20 hours..... Factor in leave and the average was about 23 hours per month.
Just checked mine and much the same - seem to remember we got down to 15 hours a month briefly at some point in the early 80's (fuel/money crisis??)...I personally totaled just short of 1000 hrs
on the F4 in 5 years...and I thought that was "thin".
10 hours a month is criminal, IMHO..
Best Rgds.