Pheidippides did in fact run that distance that is now called a marathon - so your response is 'null and void'.
Pheidippides did in fact run that distance that is now called a marathon - so your response is 'null and void'.
Assuming someone did run from Marathon to Athens, it would have been a trail marathon or a dirt road at best with carriage ruts and uneven terrain. He would have been running in leather sandals. The ancient roadway would have wound along the curves of the terrain so the distance might have been more than the... what?... 25 miles or so that it is today.
Plus, he didn't have to beat another runner. All he had to do was beat a fleet of ships that had to sail around Sounion to get to Athens. That would have taken about a day.
I'd guess a time of four hours or longer.