How long does it take to run 26.2 miles?
There was an algorithm which looked at the number of training miles per week and the average pace per week's mileage, giving a ballpark time, ceteris paribus. A person, with no training, was estimated to be able to finish the classic marathon distance of 42.195km/26.28176mi in the 7 hour range.
Having said that. the world best time for the marathon distance on a record- eligible course, in a race situation, is a sliver over two hours (2:01:39). The fastest time for the marathon distance, however, is two hours and five seconds.
So it is highly likely that your time would fall somewhere in between those two extremes.