You're welcome!
I would plan for 1.75 hrs/lb @ 225* smoke chamber temp for getting the flat to 180* and that should leave you with some time to spare, but it depends on the thickness of the fat-cap, smoker and weather related conditions as well.
Oh, don't think I mentioned it, but if you score the fat-cap in a cross-hatch fashion about ~3/4" between cuts, it will aid in rendering-down the fat for self-basting during the smoke...smoke with fat-cap up. You can work the dry rub into the cuts in the fat as well for an even heavier bark, if you like. Not to mention, it's looks pretty darn cool when you pull it out of the smoker and see how the fat looks like a distorted checker-board pattern.
Oh, the point can be monitored instead of the flat, and do the seperation when the point is about 160*, or just a touch under. Just stab the flat and get a temp reading before you bring it out to seperate, so you know if it needs more time to hit that 180* mark. I've found that if I wait until the point is around 170* or higher, the burnt ends don't have quite as good of texture. I try to get them so they have a slight snap in the interior chew, and 160* before cubing for the second smoke seems to be pretty close to that sweet-spot.
The flat may not quite be up to 180* when the point hits 160*, but you can always toss it back in after seperation, which only takes about 30 seconds if you know what to look for/where to start. Just find that fat layer between the two muscles, and once you start to cut into it from the side, it should roll open nice and easy with little knife-work. The muscle fibers run perpendicular to each other between the point cut and the flat cut, so they're easy to distinguish. Also, the point has much more intermuscular fat and tubular muscle construction, while the point is more fibrous and much leaner.
It's kind of sixes on monitoring the temps this way, but, you can get great burnt ends and great sliced flat to boot.
Hope that helps with the burnt ends adventure...it's pretty easy, really...don't get flustered about it if the point gets away from you on temps before cubing...it's not like anything will get ruined, it just won't be what I consider the ideal temp for BE's. Oh, if temps do go much over 170* in the point before you cube, then run shorter time on the second round of smoke for the cubed point...about 1-1/4 - 1-1/2 hours, depending on cube size. Otherwise, from the 160* or under temp, 2 hours is about my target, with a quick peek at 90 minutes for color. If it's getting slightly carmelized, or even to the point of getting very dark colored before I yank 'em out, that's perfect...should have a slightly crispy outside (or for very crisp, just go a bit longer), with a snappy chew inside...almost like multiple mini-popping between your teeth with every chew...that's my idea of the perfect burnt ends. I don't get 'em that way all the time...that's pushing perfection to nearly un-measurable limits...maybe 3/4 of the time for me, so don't get discouraged if it doesn't end that way for you. Part of the fun is trying to get that texture, and duplicating it the next time.
Gee-whiz...can't tell I like a good brisket smoke, huh? LOL!!!
Have fun, fellow smoker!
Eric