For all you Incline Treadmill Walkers, a quick ?

For all you guys that use this as your cardio at what pace do you walk(mph) and at what incline??? I dont have a heart rate monitor so if that is how you guys guage it then I am out of luck for now. Also, I want to be able to do my cardio in the AM on an empty stomach but that will not be possible every day. I may be able to squeeze in 2-3 days per week of AM cardio but the other days I will have to be doing it at night after my workout. On the days that I can do it in the AM I will be going for 40-60min but how long would you guys think I should do it when I am doing it post workout??? This will be my first time using low intensity cardio so I am not sure. I normally always have done HIIT, moderate jogging, or just strait out sprints. But wear and tear on my joints has made me decide to do the incline walking instead. By the way I will be doing 5-6 days per week of walking, I am 23 years old, 5'5", 177lbs, 12%BF.

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I usually go at 3.7 mph and work my way up to 10-12 incline (move up 1 incline every 1 min, quicker in the beginning and slower as it goes on) then stay for about 10mins and then start my decline down (move down 1 deline every 1min) That gives me about 30-40 mins. Sometimes I only go up to 7 and stay there for a while, or I go up to 15 (the max) and do 4mph for about 10 mins, with a cool down, that is when I want a short intense session.

Pain

3.0 up to 15 incline on AM cardio
After workout my heart rate is already up so it goes 3.0mph up to about 7-8 incline.

Thanks guys for the suggestions