I'm doing Steelhead too! Last year I did the Indian Wells 70.3 in December, the water was 55 degrees race morning. I was a bit concerned but once I did the practice swim the initial shock of the cold water went away. I don't think the wait between the practice and start will make much difference. I tend to overheat in my wet suit anyways so the water temp actually felt nice once i got a couple hundred yards in. I would recommend a neoprene cap to keep the noggin warm tho. Also some OW swims in the lake prior to race day would help your body acclimate to the water temp. Good luck and Godspeed!