A 5 hour marathon is 11:27 per mile, or 7:07 per kilometer, for 26.2 miles: 10K in 1:11:06, halfway in 2:30:00 and 20 miles in 3:48:51.
The exact pace is 11:26.5 per mile, so the rounded 11:27 held all the way finishes in 5:00:12, just over five hours. 11:26 per mile finishes in 4:59:46, and 11:22 per mile in 4:58:01.
If you plan a 5 hour marathon with run/walk intervals, the intervals change the running pace you need. Running 4:00 at 10:30 per mile and walking 1:00 at 15:00 per mile averages 11:10 per mile, a 4:52:52 marathon. The same intervals with the running at 11:00 per mile average 11:37 and finish in 5:04:39, over the goal. Try your own intervals in the run walk pace calculator.
The tables list the clock time at each marker for an even pace and for a 2% negative split, which runs 11:33 per mile to halfway (2:31:31) and 11:20 per mile after. If you run/walk, compare your elapsed time with the table at the markers rather than your pace at any one moment: the average is what counts.
Check the race's time limit before you choose a goal. It is set by each race and published in its runner information, and some courses reopen roads to traffic behind a sweep vehicle. For other finish times, the marathon pace chart runs to 6:30.