Is your gym pool only 3 lanes? If so, I would think you may have a problem with it being full. I also would expect people to jump in and walk/jog/splash around, during that time in lane 3. So bad form? No, but I think you will encounter some members that want to use the pool at that time who may not like it. They may assume you are with the masters class and wonder why you are not in those lanes. Just my opinion.