To make it complex, ~90% of RAAus aircraft have just a gauge on the VDO / Rotax branded hour meter that ticks over as soon as the engine starts. Add to that, some of them have a flight/air-switch that starts ticking over when the aircraft exceeds a specific speed. Some maintenance organisations use that figure for engine maintenance.
Some manufacturers such as Jabiru, specifically state that the engine maintenance must be based on the VDO time, which is engine runtime hour-for-hour. Otherwise, if the aircraft is a circuit queen in a training environment, it could hit the 1,000 TBO and have actually had the engine running for 1,400 hours.