When you say meat birds some will assume you mean Cornish cross.
But generally any breed of chicken can be called a meat bird, if it's raised for the pourposes of producing meat.
Since you are planning to Smoke the meat, a slow cooking method is going to be used, and if you are not plannning to sale them, but want the best tasting meat. I would go longer then the recommended time before butchering.
In our case feed cost to weight ratio is not a factor, so we go longer then what most people recommend. We also don't sale our meat.
Most Generally It's recommended here that you raise cornrish cross 6 week before butchering. I would go long maybe 10 to 12 weeks, but slow there growth by having feed available only 12 hours a day.
For standard breed I would also go beyound the recommend 12 to 15 weeks, to about 18 to 22 weeks, and make sure the get some sort of grass.
One last item but not the least important, do you plan on butchering them yourself or having someone else do it. You need to decide that before you get your chicks. If you plan on doing it yourself, how many can you do a in a day? If you plan on having someone else do the butchering, you need to find someone first, as that will reduce your stress when it comes time to butcher.
I wouldn't put Cornish crosses on grass until they are fully feathered, usually after 2 weeks or so.
Tom