I look at oiling a bit different. Here's why.
In the last several months I'd cleaned, oiled, and greased a bunch of machines. Set them aside while waiting for accessories or parts or something. Then when we took them out to finally use them I checked to see if there is any oil showing on the moving parts. If the machine looks dry, I oil it.
Every 8 hours of use sounds good if you can remember how long you sew each time. If you sew a lot each week, then oiling it once a week sounds reasonable to me.
Joe