This is what I use in my weather station code 
long sys_sunrise = sys["sunrise"]; //  json return value for sunrise
String Sunrise = String(hour(sys_sunrise)) + ":" + String(MyPrintDigits(minute(sys_sunrise)));
 
long sys_sunset = sys["sunset"]; // json return value for sunset
String Sunset = String(hour(sys_sunset)) + ":" + String(MyPrintDigits(minute(sys_sunset)));
//add '0' before digit
String MyPrintDigits(int digits) {
  String new_digits = "";
  if (digits < 10) new_digits += "0";
  new_digits += String(digits);
  return new_digits;
}