How does localization affect when day-specific annoucements are seen?

Question

Facebook publishes announcements/reminders for day-specific events like birthdays. Does localization affect when these are seen?

For example, if my birthday is February 1st, would a friend in another time zone see the announcement starting at Feb 1 their local time, in my time zone, or at some other time zone (e.g. Greenwich mean)?

Any option seems to have drawbacks:

• If announcements are based on local time, a friend who lives in India may see the announcement the morning of February 1st for him, but I'd get it in the evening of a previous day. Or if they lived in Japan they might not see it until the evening of Feb 1st, when it's already Feb 2nd for me.

• If announcements are based on my local time then the friend may be confused about when my birthday actually is, as the announcement will show up for them for at least part of a different day.

_{For a birthday announcements these aren't very serious concerns; it's just an simple example to clarify the question}

Answer 1

I think the question pretty much describes the dilemma, which has no good universal selection. In the birthday example, the problem is in the vague definition of “birthday”; it is a social convention more than anything else.

If you consider something more objective, like a “one-day offer” by a company, then it becomes even more obvious that the crucial issue is how things are defined. In global consideration, a company should define when the offer is valid (e.g., on a particular day in a particular timezone) and announce it accordingly.

The programming challenge is then to implement this properly. Mostly, it is a matter of making time references relative to a specific timezone, or the user’s timezone. These typically require different approaches: server-side vs. client-side. (The server timezone might not coincide with the intended timezone, but they should have a defined relationship.)