You can do HIIT: 10s warmup and 4 sets of: 30 second high intensity work followed by 30 seconds break. That's 4m10s in total.

It's been clinically proven to help with vascular health (HDL cholesterol level goes up) and increase insulin receptiveness.

After quitting full time job in 2000 I started with 1 hr but very low intensity. After 3 month I've lost all of my pounds and was able to go for however long I want. Like 200km bike ride.