Weekly play is roughly 7 days apart; fortnightly play is 14. Longer gaps may include holidays or games that were not recorded.
What this measures
Order distinct session dates within each campaign using recording start dates, not upload dates. Calculate positive gaps between consecutive dates within the snapshot window, average within each campaign, then average across campaigns. Requires at least two recorded dates per campaign. Unrecorded games and gaps crossing the window boundary are not observed.