Usually October? right before frosts become common. Learned that straight 30 oil was not a good idea in a pull start mower.
In a bit of a drought right now, so it's possible that the last mowing for this year was... July? I honestly don't think I mowed last month, and other than one small patch, still don't need to. Been too dry. Might run the mower just to pick up leaves, not for the grass.