billed hour vs. machine hours

My year end was the end of January so I was looking at invoices and inspection logs I did a little bit of math and found that over the last year I had about 80% machine time vs. billed hours. I didn't go any farther back to see if it was a one off or if it represents the norm.
I wonder if my numbers might be skewed a little because I do a lot of work for Mennonite community and most of my jobs for them are 2 hrs and 59 minutes or just over but not enough to charge another 1/2 hour

billed hour vs. machine hours