Audit and fix date and time handling across my app. Find every place dates are stored, compared, parsed, and displayed: database columns, API payloads, form inputs, emails, and UI rendering. Standardize: store all timestamps in UTC using a real timestamp type (never local time, never strings); convert to the user's timezone only at display time; use one date library consistently instead of mixing native Date parsing with library parsing; validate date inputs explicitly instead of relying on Date parsing, which accepts surprising strings differently across runtimes; and check every date comparison for timezone mistakes, like comparing a UTC timestamp against a local midnight. Audit boundary cases: subscriptions renewing at midnight, daily limits, anything that buckets by day, since those break for users ahead of or behind server time. Don't change business logic about what dates mean; fix representation and conversion only. If a column already holds ambiguous local times, write a migration plan for it and flag the ambiguity instead of guessing the intended timezone. Deliver: the storage and display standards applied, the list of timezone-sensitive comparisons fixed, the migration plan for any legacy columns, and verification: set a test user to a timezone 12+ hours from UTC and confirm dates render correctly around midnight.