Hi CR,
When I was on the B747 classic for a large cargo company I typically flew up to transitition altitude (usually around 18,000) and then after descent from transition level (below 6000). I hand flew much more than most did but I liked to keep proficient. Being on the high side I bet it was 10-15 minutes per leg so about an hour or so per month out of 50 hours of block time.
