I've been lurking on this thread for a while now, as I've got a Concept 2 rower in my garage, and I try to use it in the winter months when my cycling mileage takes a nosedive. I started back on the rower about ten days ago, and my usual (fairly unstructured) strategy is just to warm up, then to row for 30 minutes at a pace that I can sustain for that length of time. I'm a relative lightweight (around 71 kilos), and I'm also an old git (just turned 59).
Tonight I had my first attempt at a time for 2000m - it took me 8:22.9, and I definitely went off too fast at the start, so I was really struggling to maintain the pace towards the end. I'm aiming to get under 8 minutes, so watch this space! Don't hold your breath though - it may take a while to reach my goal.