This aerobic exercise should be completed at 60% of YOUR maximum effort, an RPE of approximately 3.
Start at whatever level works for you. If you are in rotten shape and carrying a lot of extra weight, it may be only 5 minutes a day. Keep your heart rate in the target zone and keep showing up, every day, until you can do 30 minutes a day.
RPE stands for Rate of Perceived Exertion and is based on a 10-point scale.
10 = extreme exertion -- conversation is impossible
8 = high effort -- conversation is extremely labored
6 = optimum effort -- conversation is difficult, but possible
4 = medium effort -- conversation is easy to maintain
2 = warm up