Cooking Time when splitting a Brisket???

Think of it more like 2 smaller briskets. But extend the expected time a little because of the smaller smoker. I'd bet they take between 12 and 13 hours to complete. This is if you crutch at 160 or so..

 

Hi there and welcome!

At a smoker temp of 275F you can expect around 1 hour a pound (probably a hair over). Even if you cut it in half I don't think you would save a massive amount of time. The solution is to know you will finish about 4-5 hours before you plan to eat. If the smoke runs long, well you've got 4-5 hours of cushion.
If the smoke ends on time then you double wrap in foil, wrap in 3 bath towels, and set on the counter for the 4-5 hours and then unwrap and slice at the time to eat. It will still be piping hot!

Now I always recommend people trim their brisket so that the thinner portion of the flat is removed and what is left is a nice aerodynamic fairly uniform piece of meat, and they re-purpose the good trimmed away meat.
If you leave that thinner stuff on it just drys out and/or burns up and is tossed away in the end anyhow.

Here is the diagram I always share to give a visual of what I mean:

If you trim like this you may find that your brisket fits as a whole into your smoker! Also you could aggressively trim like this and MAKE the brisket fit in your smoker as one piece rather than separating the point and the flat... which as a Texan I would never recommend

In my thread here: https://www.smokingmeatforums.com/threads/my-brisket-flat-trimming-approach-explained-qview.286564/

I discuss the trimming in detail as well as what you can do with that good extra meat you trim away. I personally just roll/fold it up and throw it in the foil pan, along with trimmed beef fat, that I smoker my brisket over. The meat comes out as either burnt ends, super tender shredded brisket, or a combo of both
That thread I posted will explain it all but here is another visual of what I mean.

I hope this info helps you out!

 

If you don't need the whole brisket I have been saving the flats and making corn beef from them. I find it still takes about the same time to smoke as if it where whole.