We had a user that was having issues when configuring a tag with a specific start date and end date.

While investigating this issue, I found that the Start and End time for a Tag that is stored in UTC will be treated as that time in any timezone and not be converted to that visitors timezone.

For example, if we create a Tag such as the following:

In the above example the start date is set as 1 AM July 14 NZST with end date 8 PM July 14 NZST
When this is converted to UTC, the start date is 1 PM July 13 UTC with end date 8 AM July 14 UTC

When we then test this tag in the browser, the tag does not fire with the following in the logs:

not firing as this tag does not match date
However, the time of my device when testing was 11:20 AM NZST or 11:20PM UTC

When I changed the End Date of the tag to one day further (8 PM July 15 NZST, 8 AM July 15 UTC), it fired correctly as it detected the End Date time had not occurred yet:

This indicates that the time for the start/end date is converted to UTC but is used in the browser as the local timezone of the browser.