Always cook to temp not time, especially when it comes to chicken breasts. Others like ribs, brisket, pork butt, etc need further testing, but that's another subject.
Don't use the recommended times from the instruction manual but come to this forum and find your information. Times should be used for ballpark planning not final results. Temp/testing should be used to determine when product is ready.
If you have a remote therm, test probe in boiling water (212*) and ice water (32*), then place it in your smoker to compare accuracy of the smoker therm.