An attribution window is a policy choice informed by behaviour. It is not a neutral setting. Longer windows credit more outcomes to campaigns, while shorter windows can miss genuine consideration journeys.
Begin with the natural delay between discovery, installation and the conversion you care about. Compare distributions by channel and conversion type. A registration may happen within minutes; a paid subscription may reasonably take days.
Document separate windows where the business case warrants them, and keep the rule stable enough for trend comparisons. If a platform applies a different window, label that distinction in reporting rather than blending unlike figures.
Run sensitivity checks before changing policy. Show stakeholders how one-day, seven-day and longer windows alter attributed volume and efficiency. The most useful choice is the one teams understand and can apply consistently.