several years ago I was a marshall for the elite series tournament on Amistad. I believe it was in late February. the entire tournament was held with temps in the 30's and sleet the first morning. the pros did find a few on beds, but not many. during the practice period before the tournament, the temps were in the 70's and 80's and fish were on beds all over the lake.
I guess the best answer to your question would be to watch the forecast for that region, and try to pick a time in late Feb/early March when the temps have been warm for several days.