If your young and semi fit you might get away with it under 2hrs,
I would start with 3 runs a week with 2 of them at a nice steady consistent achievable pace of no more than 30mins and one hard interval session of 15-20mins then increase the time by 10mins each week for the longer runs leaving the interval session at 20mins (These are hard on the body and you will need a day to recover properly from it)
Oh and the hardest bit will be sorting your diet out if its bad atm
Good luck, let us know how you get on.
I would start with 3 runs a week with 2 of them at a nice steady consistent achievable pace of no more than 30mins and one hard interval session of 15-20mins then increase the time by 10mins each week for the longer runs leaving the interval session at 20mins (These are hard on the body and you will need a day to recover properly from it)
Oh and the hardest bit will be sorting your diet out if its bad atm

Good luck, let us know how you get on.