I did some work in an speed shop a few years ago and when we built race engines there was never a 'break in' period. With roller cams, once we started them and got them up to temp and checked for leaks, overheating, etc we would go straight to dyno pulls or in the car and race. With cylinder finish and rings these days they will seat fast. If it were my boat, after I had it running on land, Id put it in the water do a half dozen 1500 to WOT runs and call it good then use it how you want. I know that's not what manufcturers say, but in reality if its gonna break its gonna do it right away running it easy for a given amount of time isn't going to change that. If its flat tappet, then you need to take care to get the cam broke in, but even at that 20-30 minutes and run with it.