What is the easiest way to achieve a state of no physical suffering? I read that those monks who self-immolated probably felt no pain because they were in nirvana...

Is there a state you can get to more easily than nirvana where you can be conscious and pain-free? If so, how many hours of meditation do you need to get there, on average?
You can reach states after a couple of years of practice where the "suffering" caused by pain is mitigated to a degree.  The sensation of pain is still there, however.  The only state I've read of where pain might not be felt is in nirodha samapatti.  Here, feeling and cessation cease.  In fact, the consciousness stream temporarily ceases almost as if you were dead.  I don't think you can put a number on how many years (lifetimes!) it would take to reach that state.  It's only available to one who has mastered the other eight absorption (rupa and arupa) and then possibly only to those who have reached the stage of arahantship or non-returner.  See MN 111 for a description of Sariputta entering this state and the Visuddhimagga at XXIII for a gloss of nirodha samapatti.