Shibuya Crossing is a real time commitment — fit it in only if it's a priority.
Allow 20–30 min.
When the lights change, a thousand people surge from every direction and somehow nobody collides — for two minutes it's the most Tokyo thing you'll see, and it's free. But it's literally a crossing: you watch it, snap it from the Starbucks or the Sky deck, and you're done in ten minutes.