I'm looking for a man that runs in Hyrule Field to that I can sell him a bunny mask, but I can't seem to find him. At what point in the game can he be found? Does he have a set route that he runs at certain times? Does playing the Sun and Moon Song change his schedule? I've ruled out finding him as old link because only young link can wear the mask.
The running man follows a path around Hyrule during the daytime. Once the sun goes down, he'll sit down to rest, enabling you to interact with him. If I recall correctly, you can catch him near the side of LonLon Ranch which faces the entrance to the Lost Woods, so if you wait a while there, he should come by. At this point, you simply have to follow him until nightfall, wearing the bunny mask. Make sure you are wearing the bunny mask when you talk to him, as well.
Note You must be playing as young Link to find him in this manner, but you must have already completed the first three temples.