daylight savings from calander

I don't know, maybe there's a way .net knows these things?

If someone enters the value on a local PC, you could get DateTime.Now and check the value of IsDaylightSavingsTime. If they are entering values on the Web from possibly different time zones, you won't know unless you ask (or have some background check).

The better way to track time like this would be to store the UTC time which is the basis for the DateTime class. The you can convert it to local time (including DST), perform operations, etc.

It's not clear what you are doing with the array of time zones. Please explain if I haven't answered your question already.

<<It's not clear what you are doing with the array of time zones.>>
I'm adding or subracting based on PST, EST and 50 other time codes.
Let's say for example it's daylight savings tomorrow in the time zone and a person says "send me an alert at 10:00am tomorrow", I add the time difference based on the current time difference, but tomorrow the time difference is different.

How can I tell the daylight savings time of the time the person want's the alert.

Like if they want monthly alerts or weekly alerts, the time in the database has to be changed when the time changes.

Is there a way to make that more effecient, and how do I tell when daylight savings time changes for every time zone?

This depends on how the alert is activated. I would guess there is a background thread running for each client that compares the desired date/time of the alert to the current local time.

You might find this article interesting:
http://msdn.microsoft.com/en-us/library/bb397781.aspx

Using the TimeZoneInfo objects plus the classes DateTime and TimeZone, you should be able to get where you want to go, but again I question how this is implemented.

Thanks Deric, that will give me the time zone at that time, but what if the time changes?

What I'm doing is using a global timer, because users most likely won't be logged in to the web site when the timer is due to be activated.

I'm just calling all times greater than the current time from the database.

If the timer is periodical, then it resets the time for that client.

So how does the server know what time it is for a client? Is this based on reading the time on the client's machine when he logs in, or is this based on some stored value for time zone for each client, or something else?

It's based on a timezone stored in the database for his login and then a calendar entry.

OK, got it. So I imagine your app should do something like this:

for every "tick" of the clock
  for each alarm in queued alarms
    convert current UTC time to the time zone for this alarm
    if current time in new time zone is past alarm time
      send alert

The third line is probably the question. Take a look here
http://msdn.microsoft.com/en-us/library/bb397769.aspx

Note this only works with .NET Framework 3.5 or later.

Yes, I'm using .net framework 3.5
The catch is, that I don't want to chew up processing time by iterating through each alarm record.

I just want to able to have the right times stored in the database and say is alarmtime >= currenttime.

Is there a way to do that?