What does it mean that reward timing is critical?

Rewards that come immediately after the routine are most effective for habit formation.

Example: Two people start a running habit on the same January morning. The first runs because she wants to lose twenty pounds — a reward that lives weeks or months in the future, invisible after every individual session. She finishes her run, towels off, and feels nothing except sore legs and the faint guilt of knowing she ate pasta last night. By February she has stopped. The second runner finishes each session and immediately opens a notebook where she draws a red X through the day, fills in her distance, and writes one sentence about how the run felt. The X is satisfying. The data is satisfying. The sentence creates a tiny narrative of competence. She does not care about weight loss yet — she cares about the X. By March she has not missed a day, and the weight loss arrives as a side effect of the streak she refused to break.

Try this: Choose a habit you are currently building or want to build. Identify the natural reward — is it immediate or delayed? If delayed, design three immediate reward candidates: one physical (a sensation or action you perform right after), one visual (something you see or log), and one narrative (a sentence you write or say to yourself). Test each for three days and note which one creates the strongest pull to repeat the routine tomorrow. That is your timing bridge.