You need to press the button once the target and the arrow are in the exact same position. You can use a ruler as a guide over your computer screen if you don't have good precision 😉
Hi! My friend and I got stuck on this sequence for ages as well, until I read this comment. It was really easy once we knew we just had to line the target and the red line up together, but we assumed we had to account for the bullets' travel time, so we got stuck. If you ever update Chapter 3 again I think it would help a lot if you made it clear that you need to line the targets up with the arrow. Anyway, thanks!