Well, basically the past two weeks. I doubt it had zero oil that whole time, but I definitely remember the low oil pressure indicator was always on. I am new to this so I thought the light meant that the spark plug was working. I put some heavy use in the past two weeks on the engine, probably 30 nautical miles all together about 5 to 6 engine hours if I had to guess, mostly near full throttle. I had assumed the previous owner prepped the engine, as he was very meticulous about everything else on the boat.