I would think you would know your boat's engines like you know your others. A Car that uses no oil between 3000 mile changes, only gets a check and look for leaks the next day after a change (to look for leaks around filter & drain) and about half way to the next oil change, If you have a car that uses a quart every 2000 miles you check it more often ,every 500 to 1000.
I would be more concerned about the much more costly and usually larger marine engines, but depending on consumption, when prudent. Oil consumption from an engine burning it will usually be at a predictable hourly rate. It's the failures that sometime occur that I would spot check for.
I would check when they are shut down and cooled off a little. How often? Well, get to know your cast iron and forged steel!!!
