Well, it depends on your level of fitness and to some extend your height. If your a tall guy, you're a better rower from start, because you pull longer and harder, thus gain more momentum with slightly longer rest intervals.
Anyway, it's a hard question to answer, but I think that if you do an all out effort for approx. 1 1/2-2 minuts, you'd probably have rowed 500 meter. It's a bit more trickier with longer distances, as 1000 meters and above, because if you start out too hard, you really nosedive in the last half, which affects your time noteably. But my best guess would be something like a steady pace of one stroke per 1,5-2 seconds for 4,5-5 minuts will have gotten you the 1000 meters.