Short answer
Why Are My Automation Dates Off by One Day?
Automation dates shift by one day when a date-only value is interpreted as midnight in one timezone and converted to another, or when daylight-saving rules are applied inconsistently. Identify whether the source is a date or timestamp, choose one authoritative timezone, and format the destination only after conversion.
Common causes
- A date-only string is parsed as midnight UTC and displayed in a negative offset.
- The source, automation account, and destination use different timezones.
- A Unix timestamp is interpreted in seconds instead of milliseconds.
- Daylight-saving transitions make fixed-hour offsets wrong.
Diagnostic steps
- Capture the raw source value, including its offset or lack of one.
- Document the timezone setting for each system and the intended business timezone.
- Parse timestamps in their declared timezone, convert once, then format for display.
- Test dates near midnight and daylight-saving transitions before publishing.
Example
“2026-10-01” becomes midnight UTC and displays as September 30 in Los Angeles. Treat it as a date-only value instead of converting it as an instant.
Caveats
Date-only values and timestamps represent different concepts. Appending Z or a guessed offset can silently change the business date.