Some BIOS's do in fact support timer-based wake-ups, but as far as I know  
there's no Windows API support for setting that (of course it would have  
to be set while the computer is awake, since when it's suspended --  
hibernating or just on standby -- no code is executed).

If it does exist, I would expect to find it in something related to ACPI,  
probably in the WMI classes.  Unfortunately, I don't use WMI and so don't  
really know what the best way for finding specific WMI support in the docs  
is (all I can find is the general purpose "System.Management" namespace,  
with various abstract classes and APIs for accessing objects that I don't  
find documented).

Pete

Nothing in the framework, so you'll have to "PInvoke" a bit.
The API's you need to call are CreateWaitableTimer and SetWaitableTimer.
Following is a complete (Q&D) sample that illustrates how you can set a
system to be awoken from sleep/hibernate using above Win32 API's.
Note that here I'm setting a relative wakeup time of 300000000 nSecs.
That means that the computer will wake-up (supposing he's asleep or
hibernating)  within 30 seconds after setting the timer.
Consult the MSDN docs for details on SetWaitableTimer and it's arguments.

using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Threading;
namespace Willys
{
class Program
{
   [DllImport("kernel32.dll")]
   public static extern IntPtr CreateWaitableTimer(IntPtr
lpTimerAttributes,
   bool bManualReset, string lpTimerName);

   [DllImport("kernel32.dll")]
   public static extern bool SetWaitableTimer(IntPtr hTimer, [In] ref long
   pDueTime, int lPeriod, IntPtr pfnCompletionRoutine, IntPtr
lpArgToCompletionRoutine, bool fResume);

   [DllImport("kernel32", SetLastError = true, ExactSpelling = true)]
   public static extern Int32 WaitForSingleObject(IntPtr handle, uint
milliseconds);

     static void Main()
     {
           SetWaitForWakeUpTime();
     }

       static IntPtr handle;
       static void SetWaitForWakeUpTime()
       {
           long duetime = -300000000;    // negative value, so a  RELATIVE
due time
           handle = CreateWaitableTimer(IntPtr.Zero, true,
"MyWaitabletimer");
           SetWaitableTimer(handle, ref duetime, 0, IntPtr.Zero,
IntPtr.Zero, true);
           long duetime = -300000000;
           Console.WriteLine("{0:x}",duetime);
           handle = CreateWaitableTimer(IntPtr.Zero, true,
"MyWaitabletimer");
           SetWaitableTimer(handle, ref duetime, 0, IntPtr.Zero,
IntPtr.Zero, true);
           uint INFINITE = 0xFFFFFFFF;
           int ret = WaitForSingleObject(handle, INFINITE);
           MessageBox.Show("Wake up call");
       }

}

Willy.