[berndao]

Okay, ich habe wohl eine Lösung gefunden:

//+------------------------------------------------------------------+
//|                                                        Test3.mq4 |
//|                        Copyright 2020, MetaQuotes Software Corp. |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2020, MetaQuotes Software Corp."
#property link      "https://www.mql5.com"
#property version   "1.00"
#property strict

datetime LastActiontime;

//+------------------------------------------------------------------+
//| Expert initialization function                                   |
//+------------------------------------------------------------------+
int OnInit()
  {
//---
   
  Print("Start Time is= ",TimeCurrent());
  LastActiontime=Time[1];
  Print("die Zahl ",1.23456789," gerundet auf die ",_Digits,"te Nachkommastelle ergibt ",roundD(1.23456789));
   
//---
   return(INIT_SUCCEEDED);
  }
  
  
//+------------------------------------------------------------------+
//| Expert tick function                                             |
//+------------------------------------------------------------------+
void OnTick()
  {
  if(LastActiontime==Time[1]){
    return;
   }
   else
   {
     LastActiontime=Time[1];
   }
   Print("Last Bar Time is= ",Time[1], "and last Close Price is= ",Close[1]);
  
  
//+------------------------------------------------------------------+
}


double roundD(double number){
  double n=number*MathPow(10,_Digits);
  int b=MathRound(n);
  double c=b;
  double result=c/MathPow(10,_Digits);
  return result;

}

Letztlich habe ich eind datetime Variable, die trackt ob sich seit dem letzten Tick die Open Zeit des letzten balkens geändert hat.
Nur dann wird der Code ausgeführt.