Alterando a Data do windows com Delphi

function SystemDateTime (tDate: TDateTime; tTime: TDateTime): Boolean; 

var 

  tSetDate: TDateTime; 

  vDateBias: Variant; 

  tSetTime: TDateTime; 

  vTimeBias: Variant; 

  tTZI: TTimeZoneInformation; 

  tST: TSystemTime; 

begin 

  GetTimeZoneInformation(tTZI); 

  vDateBias := tTZI.Bias / 1440; 

  tSetDate := tDate + vDateBias; 

  vTimeBias := tTZI.Bias / 1440; 

  tSetTime := tTime + vTimeBias; 

  with tST do 

    begin 

      wYear := StrToInt(FormatDateTime('yyyy', tSetDate)); 

      wMonth := StrToInt(FormatDateTime('mm', tSetDate)); 

      wDay := StrToInt(FormatDateTime('dd', tSetDate)); 

      wHour := StrToInt(FormatDateTime('hh', tSettime)); 

      wMinute := StrToInt(FormatDateTime('nn', tSettime)); 

      wSecond := StrToInt(FormatDateTime('ss', tSettime)); 

      wMilliseconds := 0; 

    end; 

  SystemDateTime := SetSystemTime(tST); 

end;