There are always a number of questions that arise when talking about technique on the Concept2 or Waterrower rowing machines. Most beginners make the same mistake of using their arms far too early in the stroke and not really putting much leg power into the pull. These are fairly basic errors that can be corrected by getting an experienced rower to coach you or watching a training video such as this one.
This video shows some of the common mistakes
So as you improve and start to work on your 2000m times, finer points of technique start to come into play.
Where should you pull your hand to when on the rowing machine?
Afloat you have to keep the blades in and then feather, wherever that takes your hands. Low for flat water, higher if rigged for rough weather. Most oarsmen seem to keep wrists high aground too, presumably from habit.
But on a grounded erg, no need to lift wrists, it’s much easier to keep wrists flat and all in line with the chain, as Concept2 writes, so that there are no bending moments anywhere. Any extra length from cocking the wrists can only be small and at the expense of small muscle-tendon units in the forearms, so not worth it and possibly risky as noted above. Better save a little time to get in an extra stroke done full body.