Thank you for your replies, here is a picture of the journey
11 mins connection in Serbia is pretty risky and note that there is not much in Rakovica maybe go till Belgrade and spend there asome time and take a later train or next day one :)
The tickets in Montenegro and Serbia are pretty cheap (If you have a flexipass save these traveldays as the tickets are cheaper as the value of a Travelday ) Podgorica - Belgrade is just 19.20€plus reservation :)