How long does it takes to travel from Mangalore Junction Station to Mangalore Central Railway Station?
What is the distance? What modes of transport are available and what is their price?
Are local trains available at all times?
It's 5 km between the two stations and the best way to get from one to another would be to get a rickshaw ride. It would probably be around 50 to 80 rupees depending on your bargaining skill.
If you don't have too much luggage, you could opt for a bus, which is, I think 10 rupees.
I imagine it is possible to take a train between these stations but according to my search, there are only 5 trains daily, two early morning, one mid-day, two in the evening. Perhaps there are more trains available that aren't listed on the Indian train info website.
It's also possible to take a taxi but the price is probably double the price of an autoricksaw ride.