Setting the time programmatically in Windows 7

Not sure why it's not working for you. The following code sets the time to today's date at 4:12 PM UTC. (Worked for me)

public class Program 
{
    public struct SystemTime
    {
        public ushort Year;
        public ushort Month;
        public ushort DayOfWeek;
        public ushort Day;
        public ushort Hour;
        public ushort Minute;
        public ushort Second;
        public ushort Millisecond;
    };

    [DllImport("kernel32.dll", EntryPoint = "SetSystemTime", SetLastError = true)]
    public extern static bool Win32SetSystemTime(ref SystemTime st);

    public static void Main(string[] args)
    {
        SystemTime st = new SystemTime
        {
            Year = 2010, Month = 10, Day = 18, Hour = 16, Minute = 12, DayOfWeek = 1
        };
    }
}

According to the docs:

The calling process must have the SE_SYSTEMTIME_NAME privilege. This privilege is disabled by default. The SetSystemTime function enables the SE_SYSTEMTIME_NAME privilege before changing the system time and disables the privilege before returning. For more information, see Running with Special Privileges.

So seems like that shouldn't be an issue.

Well, if worst comes to worst, there is always

System.Diagnostics.Process.Start("CMD", "/C TIME 19:58");  // set time to 7:58PM

Your app needs to be elevated to change the time (since changing the time could result in activity logs etc being untrue) but not to change the time zone. Put a manifest on your application with requireAdministrator and the app will elevate. (To test this before making the manifest, right-click your exe and Run As Adminstrator. This will elevate the app just the one time. Elevating is a different thing from being launched by someone who happens to be in the Administrators group. It's about choosing to use your powers.)

Chances are the user won't like the UAC prompt, so if the time-changing is rare, split it out into a separate exe, put a manifest on the main app with asInvoker and another on the time-changer with requireAdministrator, and launch the time-changer from the main app with ShellExecute. Ideally have a button or menu item to make this happen and put a shield icon on it so that the UAC prompt doesn't surprise the user. I decline UAC prompts I wasn't expecting.