Are you trying to do this to figure out the distance, or just to
mathematically see how long it takes? If you want to figure distance, do
about five trials of stepping off paces, measuring how far you go in five or
ten paces, dividing by the number of paces, and averaging the length of one
pace. If you have a regular rhythm of pacing, you can get remarkably close.
If you are just wondering how long it takes to go from point a to point b,
it's just simple math.