Years ago all I did was flats. The flat is still my preferred part of the brisket. I have always tended to cook them the same way as I cook a packer. The time tends to be about the same but as I'm sure you know with briskets they all cook differently.
My preferred way of cooking is 180 for about 6-8 hours, then wrap, turn up the heat to 230-250, and let it go until done. I would expect around 10-12 hours.