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MQL5 ReferenceDate and TimeTimeDaylightSavings 

TimeDaylightSavings

Returns correction for daylight saving time in seconds, if the switch to summer time has been made. It depends on the time settings of your computer.

int  TimeDaylightSavings();

Return Value

If switch to winter (standard) time has been made, it returns 0.

Example:

void OnStart()
  {
//--- get daylight saving time adjustment in seconds
   int sec_dl=TimeDaylightSavings();
   
//--- create the text describing the received value
   string text=(sec_dl==0 ? "Standard \"winter\" time is used" : 
                StringFormat("Daylight saving time has been switched over. The correction is %d seconds", sec_dl));
   
//--- display a description of the daylight saving time adjustment in seconds in the log
   Print(text);
   /*
   result for "winter" time:
   Standard "winter" time is used
   
   result for "summer" time:
   Daylight saving time has been switched over. The correction is -3600 seconds
   */
  }