Hi Michael. Like the guys said, it would help to know what kind of smoker your cooking on, and also what you are cooking...but generally, don't overthink recipe directions like cooking temp and time. Those are usually just a general guide to get you close. If your recipe says 240* for six hours, don't view that as an exact...it's perfectly acceptable to run your cooker at 250 until you begin to get close to that 6 hour mark, then it becomes more about internal temperature, texture and tenderness (depending on what you're cooking, of course) to determine when your meat is done.
As an example of what I'm trying (badly) to say, a generally accepted rule of thumb on smoking a brisket is that it'll take around 1.5 hours of cook time per raw pound of meat to get it done. But that's only a general guide, and not to be taken literally. The only way to know for sure when that brisket is done is to monitor the internal temperature until it approaches 200* IT (internal temp). Even then, it's really only done when it's becomes probe tender, which could be at 195* IT, or might not happen until the IT reaches 205* or more.
That is probably a more complicated answer that you were asking for...sorry for getting long winded...but I hope that helps.
Red