Starting the trip depends on where you live, and the time depends on where you catch the train.
Penn Station to Flushing Main Street on the Long Island Railroad is 20 minutes.
I take the train from Linden, and its about 40 minutes to Penn Station. But I can read, catch up on emails, argue with people on this board, etc..... And I'm not frazzled by the traffic and the lack of parking in Flushing. Train is much cheaper too.