How to change system time in C#

The SetSystemTime() API can be used to set a new system time, and GetSystemTime() retrieves the current system time. Both APIs operate using UTC time, so when setting or retrieving system time, it is essential to handle UTC time correctly.

You can use DateTime.UtcNow to get the current UTC time in C#.

To change the system time, you would typically define a structure to pass to SetSystemTime() and call it using P/Invoke as shown below.

[DllImport("kernel32.dll")]
public static extern bool SetSystemTime(ref SYSTEMTIME time);

[DllImport("kernel32.dll")]
public static extern void GetSystemTime(ref SYSTEMTIME time);

[StructLayout(LayoutKind.Sequential)]
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 Milliseconds;

    public SYSTEMTIME(DateTime dt)
    {
        Year = (ushort)dt.Year;
        Month = (ushort)dt.Month;
        DayOfWeek = (ushort)dt.DayOfWeek;
        Day = (ushort)dt.Day;
        Hour = (ushort)dt.Hour;
        Minute = (ushort)dt.Minute;
        Second = (ushort)dt.Second;
        Milliseconds = (ushort)dt.Millisecond;
    }
}

Main method

// Change System Time
DateTime date = new DateTime(2024, 11, 5, 12, 30, 15, 0, DateTimeKind.Utc);
SYSTEMTIME systime = new SYSTEMTIME(date);
SetSystemTime(ref systime);
 
// Get UTC time
Console.WriteLine("{0:yyyy-MM-dd hh:mm:ss}", DateTime.UtcNow);    

To use SetSystemTime, your program needs administrative privileges, as changing the system time affects the entire system.