var rawFbData = {

    "wed_1_open": "17:00", 

    "wed_1_close": "02:00", 

    "thu_1_open": "17:00", 

    "thu_1_close": "02:00", 

    "fri_1_open": "17:00", 

    "fri_1_close": "02:00", 

    "sat_1_open": "12:00", 

    "sat_1_close": "02:00", 

    "sun_1_open": "12:00", 

    "sun_1_close": "20:00"

  };

​

console.log(rawFbData);

​

var formattedData = {};

for (var key in rawFbData) {

  if (key.substr(-5) === '_open') {

    var openDay = key.substr(0, 3);

    var openTime = rawFbData[key];

​

    var endTimeKey = key.replace('_open', '_close');

    var endTime = rawFbData[endTimeKey];

    var formattedDataKey = openTime + ' - ' + endTime;

    if (formattedData[formattedDataKey] === undefined) {

     formattedData[formattedDataKey] = []; 

    }

    formattedData[formattedDataKey].push(openDay);

  }  

}

​

//console.log(formattedData);

​

for (var formattedDatakey in formattedData) {

  var formattedDatakeyLen = formattedData[formattedDatakey].length;

  if (formattedDatakeyLen > 1) {

    var firstDay = formattedData[formattedDatakey][0];

    var lastDay = formattedData[formattedDatakey][formattedDatakeyLen - 1];

    console.log(firstDay + ' - ' + lastDay + ': ' + formattedDatakey);

  }

  else if (formattedData[formattedDatakey].length === 1) {

    console.log(formattedData[formattedDatakey][0] + ': ' + formattedDatakey);

  }

}