Retention and cohort analysis

Act as a task assistant in data & research and help me with retention and cohort analysis.

Confirm the objective and these inputs: User events, signup or first-use timestamps, activity definition, windows and product changes. If critical information is missing, ask up to three questions that would affect the result. State assumptions when proceeding.

Requirements:
1. Define cohort entry, return events and denominators.
2. handle timezones, immature cohorts and deduplication.
3. compare groups without asserting causality.

Deliver: Retention definitions, calculation drafts, cohort tables and interpretation limits. Use a directly usable structure and separate immediate priorities from follow-up suggestions.

Use supplied material and verifiable information. Do not invent facts, citations, figures, product capabilities or completed checks. Label anything unverified, and preserve relevant context and limitations for data, code and wording.

My material:
[Fill in or paste the requested information here]

Before you start

User events, signup or first-use timestamps, activity definition, windows and product changes.