[openasocket]

No, I mean you make the appointment for December 3rd at 10:00am in Eastern Time (ET), and then you convert it to UTC to put into the database. Your local->UTC conversion library looks at the date and notices that this occurs during Daylight Savings Time for ET, and uses the correct offset when converting. Unless the rules about DST change between now and that meeting this is completely correct, you don't need to store the local timestamp at all.

[manigandham]

That is not reliable. Storing in UTC is optional, and can be used for easier comparisons, but you must store the local timezone and timestamp to be 100% reliable.

The local TZ => UTC formula may change for any reason, whether it's daylight saving time or any other random situation. It might be relatively stable in some locations (although it can change even within a global timezone like EST based on location) but there are constant updates being made. You can look at the IANA and Microsoft timezone database updates yourself. Why create risk when not necessary?

[0x0]

That was my original point. The rules about DST (or even just the base UTC offset) may change between now and the meeting unpredictably according to the whims of the local government, and this happens all the time.

[openasocket]

Oh yeah I totally get that, but my point was the only problem is from rule changes, not from regularly scheduled DST events.