When to stop HMR

When I work out using kettle bells or anything cardio related I try to use my Heart rate monitor (HRM). When I finish I am still running a high heart rate for a little while. If I keep it on for a long time and use that number am I cheating? Or should I stop the HRM as soon as I finish? I also use a Fitbit with negative calories turned on which means it will not only give me extra calories for burning but will also reduce calories allowed if I am stationary too much in the day. One last note, I input my calories burned on MFP and make sure I use the correct starting time and amount of time working out. That way I don't get double the calories added from my Fitbit.