...I think I got it on the second or third try. With one second to spare. And since the Zelda timer is faster than real life, that's about half a second. It's straightforward, but there's absolutely no room for error.
My original goal was to get the Biggoron's Sword as early as possible after becoming Adult Link, since I tend to use that thing non-stop once I get it, shields be damned. I realized that I would have to go through the sidequest to obtain Epona if I couldn't do it on foot, so I gave it a try. It was a fun challenge. I love doing stuff early and out of order, especially in OoT.