How long should a post-release comparison window be?
A useful window reflects product usage cycles, rollout shape and the speed at which the expected behaviour can emerge.
Start with the behaviour, not the calendar
A daily-use workflow may reveal adoption within a week. A monthly reporting task cannot. Define how often a qualified user has a real opportunity to encounter the change, then allow enough opportunities for a stable reading.
Account for rollout shape
A staged rollout creates overlapping cohorts. Record first exposure where possible and compare users from that point, rather than treating the public release date as a universal start.
Keep an eye on outside influences
Campaigns, holidays, outages and concurrent changes can move the same metrics. Note them in the report and use unaffected segments or earlier periods as sensitivity checks.