The following function will set the Screen Saver's time-out.
This is the amount of time, in minutes, that the system must be idle before the screen saver activates.

function SetScreenSaverTimeOut(Minutes : integer) : boolean;

var
 Sec : integer;

begin
  if (Minutes in [1..60]) then
    begin
      Sec := Minutes * 60; // Convert minutes into seconds.
      Result := SystemParametersInfo(SPI_SETSCREENSAVETIMEOUT, Sec, nil, 0);
    end
  else
    Result := False;
end;

The Minutes parameter must be between the range of 1 to 60 minutes and is the amount of time, in minutes, that the time-out is set to.

If the function succeeds it'll return TRUE, else a value of FALSE are returned.
The time-out is set, even if the Screen Saver is not enabled.

You can also use the GetScreenSaverTimeOut function (Ref. 13) to return the default Screen Saver time-out before you set the time-out. This way you can restore the previous time-out, if needed.