{
  Data sometimes have to be filtered regarding to working
  days (Mo.-Fri.) of the current Week. Following procs set
  your TDateTimePicker automatically. 
} 


function GetMonday(RefDay: TDate): TDate; 
var 
  DoW: Integer; 
  DateOffset: Integer; 
begin 
  DoW := DayOfWeek(RefDay); 
  // Montag der Woche 
  if DoW = 1 then DateOffset := -6  
  else  
    DateOffset := Dow - 2; 
  Result := RefDay - DateOffset; 
end; 

function GetFriday(RefDay: TDate): TDate; 
var 
  DoW: Integer; 
  DateOffset: Integer; 
begin 
  DoW := DayOfWeek(RefDay); 
     { 
     Friday of current week 
     Freitag der Woche 
     } 
  if DoW = 1 then DateOffset := -2  
  else  
    DateOffset := Dow - 6; 
  Result := RefDay - DateOffset; 
end; 

procedure SetWorkingDaysFilter(S, E: TDateTimePicker); 
var 
  N: TDate; 
begin 
  N      := Now; 
  S.Date := GetMonday(N); 
  E.Date := GetFriday(N); 
end; 

{Just as short as simple} 
{Einfach und kurz} 


type 
  TForm1 = class(TForm) 
    DStart: TDateTimePicker; 
    DEnd: TDateTimePicker; 
    btSetFilter: TButton; 
    procedure btSetFilterClick(Sender: TObject); 
  end; 

procedure TForm1.btSetFilterClick(Sender: TObject); 
begin 
  SetWorkingDaysFilter(DStart, DEnd); 
end;