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Dates & Time Zones

Contact and company fields​

Date/time fields of contacts and companies are stored and returned in UTC, formatted as YYYY-MM-DD HH:MM:SS (without offset). A value sent without offset is read in the instance time zone (not in the time zone of the API user); an explicit offset is applied:

You sendStored and returned (instance in Europe/Paris, summer time)
2026-09-25 10:00:002026-09-25 08:00:00
2026-09-25T10:00:00+00:002026-09-25 10:00:00
2026-09-25T10:00:00Z2026-09-25 10:00:00

lastActive is an exception: a value sent without offset is read as UTC.

Timestamps​

Timestamps such as dateAdded, dateModified or lastActive are returned in ISO 8601 with an offset, for example 2026-09-25T09:28:09+02:00. Always take the offset into account.

Custom item fields​

  • date values are sent and returned as YYYY-MM-DD.
  • datetime values are returned in ISO 8601 with the instance offset, for example 2026-09-25T12:00:00+02:00. A value sent with an offset (2026-09-25T10:00:00+00:00) keeps the same instant; a value sent without offset (2026-09-25 10:00:00) is read in the instance time zone.
  • This applies to POST /custom/item/new/{customObjectId}, POST /custom/item/batch/new/{customObjectId} and the contact customObjects payload. In a CSV import (POST /custom/object/{customObjectId}/importCsv), an offset is not applied: send datetime values in the instance time zone, without offset.