When we run in a ship engine after overhaul, we run it in over 24ish hours.

20 mins on zero load.
Have a look inside
1 hour on zero load
Have another look inside
2 hours on 10% load
4 hours on 20% load
6 hours on 50% load
Have a look inside
12 hours on 75% load
Have a look inside
1 hour on 100% load
last check over
back on line. What a c'nt of a job! It also take 2 weeks to overhaul the b@stard!