[O] Time zone support for agenda item timestamps

[Matt Curtis]

Hello,

I would like agenda timestamps to support time zones somehow, and I'm after
some guidance from org-mode developers.

My plan is to support the time offset +HHMM or -HHMM, at a minimum.

After looking at the code I believe I need to modify org-agenda-get-timestamps
quite heavily to effect this change.

Currently it looks like it scans for timestamps which match the search date
(YYYY-MM-DD), which would need to be changed to at least match adjacent
days, and then filtered after applying the time zone offset, and
finally adjusted
with the offset to match local time.

This would mean the agenda/list displays would get the same sort of results
set, as the timestamps would be adjusted back to the search date - i.e. the
search date would be considered "local time"; the change is to consider the
offset when figuring out which items fall on this date.

I have a couple of questions:

* Is this a reasonable approach? (It would slow down agenda generation
with the extra scanning and filtering)

* If not, is there another design I can look at? (I wonder why this hasn't been
done before, so I think maybe others have done some thinking about it.)

* What parts of org-mode should I be looking at to ensure this change does
not cause a regression?

cheers,
Matt