I have on occasion needed to schedule a process to run on a nightly basis, but I did not have access to the server where I could schedule a windows service. So I had to turn to using a timer object in ASP.NET to schedule the process for me.

I used the application_start method (in the global.asax) to start the timer, so that when the app stops, the schedule will start again the next time the app re-starts. The problem that I ran into though, is that I have no control over when the application starts and stops. I had to have the schedule run at a specified time each night. I came up with a couple of methods that allow me to determine what the time is currently, pass in the time I want the process to start and then pass in the interval I want to have the process repeated.

My example below uses 6:30 pm as an initial start time, with the process repeating every 24 hours. Note that all times must be calculated in milliseconds.
<%@ Application Language="C#" %>
<script runat="server">

    private void NightlyProcess(object o)
    {
        //write code to be processed at specified intervals
    }
 
    void Application_Start(object sender, EventArgs e)
    {
        System.Threading.TimerCallback tcb = new System.Threading.TimerCallback(NightlyProcess);
        System.Threading.Timer theTimer = new System.Threading.Timer(tcb, null, GetTimerInitialDelay(18,30), GetTimerRepeatDelay(24)); 
    }
 
    /// <summary>
    /// Use this function to determine what the initial delay should be so that processing can happen
    /// nightly at the time you determine
    /// instead of at the time the web application restarted
    /// </summary>
    /// <returns></returns>
    private long GetTimerInitialDelay(int hours, int minutes)
    {
        long startMS, repeatMS, currentMS; 
        //1000 = milliseconds per second
        //60 = seconds per minute
        //60 = minutes per hour
        //hours = based on 24 hour clock -- this example passes in 18 to signify 6pm
        //minutes = if you want to have the process happen at a time other than on the hour
        //this example passes 18 and 30 so the first run will happen at 6:30 pm
        startMS = (1000 * 60 * 60 * hours) + (1000 * 60 * minutes);
        repeatMS = GetTimerRepeatDelay(24);

        DateTime now = DateTime.Now;
        long currentHours = 1000 * 60 * 60 * now.Hour;
        long currentMinutes = 1000 * 60 * now.Minute;
        long currentSeconds = 1000 * now.Second;
        long currentMilliSeconds = now.Millisecond; 
        currentMS = currentHours + currentMinutes + currentSeconds + currentMilliSeconds; 
        long delay = startMS - currentMS; 
        // we have to wait until the next appropriate time to run code
        // if it is after the specified time (after 6:30pm in our case)
        // we need to take the repeatDelay time (24 hours) and add our initial delay to it (it will be a negative number)
        // this will ensure that the process will not run until 6:30pm tomorrow
        // otherwise, we just wait the regular delay and the process will start at 6:30pm today
        if (delay < 0)
        {
            return repeatMS + delay;
        }
        else
        {
            return delay;
        }
    }
 
    private long GetTimerRepeatDelay(int hours)
    {
        long repeatMS; 
        //1000 = milliseconds per second
        //60 = seconds per minute
        //60 = minutes per hour
        //hours = based on 24 hour clock -- this example passes in 24 so it will repeat once per day
        repeatMS = 1000 * 60 * 60 * hours; 
        return repeatMS;
    }
       

</script>



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