If your new to it, start off doing 10 minutes a day for about 2-3 weeks.

i wouldn't recommend starting off more than 10 minutes for 1st few weeks as your shin muscles may start to go and they may feel like you've been kicked in them for 3 hours by a Thai fighter who knocks down walls.

in your 2nd-3rd week, youll be able to go for 15 minutes, in the 3rd-4th week, you should be able to do 20 minutes and i wouldn't recommend anymore than 20 minutes, although sometimes I do 30-40 minutes which is probably why I'm so light .

The above was my routine when i hit the wall in my fitness and it changed my fitness level for ever.