Hmmm I don't really fully know what the runner's high entails. Generally it's a bit harder to keep going at the start, but at some point it's easier to keep running than to stop. That point has been anywhere from after a few steps to after 7km. Usually it's after about 1-3km that this occurs. This time around I woke up feeling quite unrested and shitty, so getting started wasn't easy. But after the first kilometer it started getting better and better, and I guess that after 2-3 km it felt really good right to the end.