It's not possible directly, but with a P/Invoke

Put these inside the class:

[StructLayoutAttribute(LayoutKind.Sequential)]
private struct SYSTEMTIME
{
    public short year;
    public short month;
    public short dayOfWeek;
    public short day;
    public short hour;
    public short minute;
    public short second;
    public short milliseconds;
}

[DllImport("coredll.dll")]
static extern bool SetLocalTime(ref SYSTEMTIME time);

And the code would be:

DateTime Now = DateTime.Now;
SYSTEMTIME SystemNow;

SystemNow.year = (short)Now.Year;
SystemNow.month = (short)Now.Month;
SystemNow.dayOfWeek = (short)Now.DayOfWeek;
SystemNow.day = (short)Now.Day;
SystemNow.hour = (short)Now.Hour;
SystemNow.minute = (short)Now.Minute;
SystemNow.second = (short)Now.Second;
SystemNow.milliseconds = (short)Now.Millisecond;

SetLocalTime(ref SystemNow);