I don't think it will take that long, 8-10 hours is my guess. Now, it might take that long if you are opening up your smoker every 2 hours. You don't need to flip but once if at all. Flipping once is mainly necessary on a UDS.
I am a fat side down guy myself but someone did a test and they could not tell the difference either way. That being said, I think the consensus on the board is fat side towards the heat which in a bandera is fat side down. The fat layer buffers the heat.
Wannabe BBQ Illuminati