4 cities world clock on m5 stack core2. CUF_24px.h is here: https://github.com/m5stack/M5Core2/blob/master/examples/Advanced/Display/Display_Unicode/CUF_24px.h

m5core2_world_clock.ino

#include <M5Core2.h>
#include <WiFi.h>
#include "time.h"
#include <Timezone.h>
#include "CUF_24px.h"

const char* ssid     = "";
const char* password = "";

const char* ntpServer = "pool.ntp.org";

// 各都市のタイムゾーン定義
TimeChangeRule JST = {"JST", Last, Sun, Mar, 1, 540}; // 日本標準時 UTC+9
TimeChangeRule BST = {"BST", Last, Sun, Mar, 1, 60}; // 英国夏時間 UTC+1
TimeChangeRule GMT = {"GMT", Last, Sun, Oct, 2, 0};  // グリニッジ標準時 UTC+0
TimeChangeRule GST = {"GST", Last, Sun, Mar, 1, 240}; // ドバイ標準時 UTC+4
TimeChangeRule SGT = {"SGT", Last, Sun, Mar, 1, 480}; // シンガポール標準時 UTC+8

Timezone tzTokyo(JST, JST);
Timezone tzLondon(BST, GMT);
Timezone tzDubai(GST, GST);
Timezone tzSingapore(SGT, SGT);

struct City {
  const char* name;
  Timezone* tz; // タイムゾーンオブジェクト
  int x;
  int y;
};

City cities[] = {
  {"Tokyo", &tzTokyo, 10, 30},
  {"Singapore", &tzSingapore, 10, 90},
  {"Dubai", &tzDubai, 10, 150},
  {"London", &tzLondon, 10, 210}
};

void printLocalTime(const char* name, Timezone* tz, int x, int y, time_t utc) {
  TimeChangeRule* tcr;        // ポインタを受け取るための変数
  time_t local = tz->toLocal(utc, &tcr);

  struct tm *timeinfo = localtime(&local);

  char dateString[20];
  strftime(dateString, sizeof(dateString), "%Y/%m/%d", timeinfo);

  // 日本語の曜日を取得
  const char* weekDays[7] = {"日", "月", "火", "水", "木", "金", "土"};
  const char* dayString = weekDays[timeinfo->tm_wday];

  char timeString[6];
  strftime(timeString, sizeof(timeString), "%H:%M", timeinfo);

  M5.Lcd.setCursor(x, y);
  M5.Lcd.printf("%s:", name);

  M5.Lcd.setCursor(x + 150, y);
  M5.Lcd.print(timeString);

  // 曜日を時刻の右側に表示
  M5.Lcd.setCursor(x + 240, y-5);
  M5.Lcd.print(dayString);

  M5.Lcd.setCursor(x + 150, y + 20);
  M5.Lcd.print(dateString);
}

void setup(){
  M5.begin(true, true, true, true); // M5Core2の場合、引数をすべてtrueにします
  M5.Lcd.clear(BLACK);
  M5.Lcd.setFreeFont(&unicode_24px);
  M5.Lcd.setTextDatum(TC_DATUM);
  M5.Lcd.setTextSize(0.3); // 文字サイズを調整
  M5.Lcd.setTextColor(WHITE);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    M5.Lcd.print(".");
  }

  configTime(0, 0, ntpServer);
}

void loop(){
  M5.Lcd.fillScreen(BLACK);

  time_t now;
  time(&now); // UTC時刻を取得

  for(int i = 0; i < 4; i++) {
    int x = cities[i].x;
    int y = cities[i].y;
    printLocalTime(cities[i].name, cities[i].tz, x, y, now);
  }

  delay(10000);
}