Day 6 is the OP Day. Especially since you can bet 300 instead of 100 on that day. Do not place 100 on Orchid unless you want to, she is only worth x10...
Edit: If you look at the predictions, Greenbell (who is almost always right) says Orchid, and Kale (who is almost always wrong) says Jingle Begonia will win.
Edit 2: Not going to give away the day this happens (not today's race), but this has to be by far the easiest prediction day in the history of swan boat races, especially if you know what I just said above....