Date and time guidelines When applying the startDate, endDate, and previousStartDate Attributes, adhere to these date and time guidelines. The way to specify timezones I wouldn’t give much bodyweight to their advice. They are saying that "Structured information markup is most very easily represented in JSON-LD format", but I believe https://addons.prestashop.com/de/seo-suchmaschinenranking-optimization/31857-automatische-google-rich-snippets-json-ld-opengraph-seo.html