JsonExample.txt

#include <ArduinoJson.h>

// Loads the configuration from a file
void loadConfiguration() {
  TimeChangeRule UST;
  TimeChangeRule UT;
  
  DynamicJsonDocument TimeJSON(128);

  file.open("TimeUST.json",O_RDONLY);
  deserializeJson(TimeJSON,file.readString());
  file.close();

    strcpy(UST.abbrev,TimeJSON["abbrev"]);
    UST.week = TimeJSON["week"];
    UST.dow = TimeJSON["dow"];
    UST.month = TimeJSON["month"];
    UST.hour = TimeJSON["hour"];
    UST.offset = TimeJSON["offset"];    //  Summer Time
  
  TimeJSON.clear();

  file.open("TimeUT.json",O_RDONLY);

  deserializeJson(TimeJSON,file.readString());
  file.close();

    strcpy(UT.abbrev,TimeJSON["abbrev"]);
    UT.week = TimeJSON["week"];
    UT.dow = TimeJSON["dow"];
    UT.month = TimeJSON["month"];
    UT.hour = TimeJSON["hour"];
    UT.offset = TimeJSON["offset"];    // Standard Time

  //}
  Serial.print(UST.offset);
  Serial.println(UST.abbrev);
  Serial.print(UT.offset);
  Serial.println(UT.abbrev);

  TimeZone.setRules(UST,UT);
}

File: TimeUT.json
{
"abbrev": "CET",
"week": 0,
"dow": 1,
"month": 10,
"hour": 3,
"offset": 60
}

File: TimeUST.json
{
"abbrev": "CEST",
"week": 0,
"dow": 1,
"month": 3,
"hour": 2,
"offset": 120
}

Intentos anteriores:
File: Time.json
{
"UST": {
    "abbrev": "CEST",
    "week": 0,
    "dow": 1,
    "month": 3,
    "hour": 2,
    "offset": 120
    },
"UT": {
    "abbrev": "CET",
    "week": 0,
    "dow": 1,
    "month": 10,
    "hour": 3,
    "offset": 60
    }
}

File: (first version) Time.json
{
"UST": ["CEST",0,1,3,2,120],
"UT": ["CET",0,1,10,3,60]
}