I agree with s_noonan, system time has no meaning in algodoo.
For example, if I want to calculate the average speed of a car.
I use the time at the beginning of the track and at the end of the track. If algodoo lags and I use system.time the result will be different, even though the car didn't drive slower or faster. The results will also be different when I increase or decrease the simulationspeed. But if I use sim.time the result will always be the correct.