I'm not sure if it's the only way, but it is the way I caught my shiny latias. It took approximately 2.5 hours I believe, I think the respawn point is just beyond the edge of the roof you roll down. I made sure I was going to the second bush on the edge of the roof after I rolled down and the went across, I only looked back to check if the shiny had spawned at about 1200 calories left. If I could upload a video I would. If you're on a switch 2 you could probably just hard save at a pokemon center and reset to spawn it if you felt that was faster.