Maps API in Google Sheets

Code.gs

var Properties = PropertiesService.getScriptProperties();

/**
 * Return rate-limited function under specified delay.
 * @param {Function} fn The function to wrap.
 * @param {string} domain The domain under which to apply the delay.
 * @param {number} delay Time (in ms) between successive calls.
 * @return {Function} The function to call.
 */
function RateLimited(fn, domain, delay) {
  var key = domain + "-lastcall";
  return function() {
    var now = Date.now();
    var lock = LockService.getDocumentLock();
    lock.waitLock(5000);
    var last_call = Properties.getProperty(key);
    var delay_exec = 0;
    if (last_call === null) {
      Properties.setProperty(key, now);
    } else {
      var next = +last_call + delay;
      if (next > now) {
        delay_exec = next - now;
        Properties.setProperty(key, next);
      } else {
        Properties.setProperty(key, now);
      }
    }
    lock.releaseLock();
    if (delay_exec) {
      Utilities.sleep(delay_exec);
    }
    return fn.apply(null, arguments);
  };
}

// Safe, rate-limited methods.
var Safe = {
  getDrivingTime: RateLimited(getDrivingTime, "maps", 2000)
};

// "hash" arbitrary number of string arguments to use as a key.
function hash() {
  var out = "";
  for (var i = 0; i < arguments.length; i++) {
    out += arguments[i];
  }
  return out;
}

/**
 * Get driving time given origin, destination, and arrival time.
 * @private
 * @param {string} origin
 * @param {string} dest
 * @param {Date} arrival
 * @return {number?} The driving time in seconds or null if no route was found.
 */
function getDrivingTime(origin, dest, arrival) {
  var directions = Maps.newDirectionFinder()
      .setOrigin(origin)
      .setDestination(dest)
      .setMode(Maps.DirectionFinder.Mode.DRIVING)
      .setArrive(arrival)
      .getDirections();
  if (directions && directions.routes.length > 0) {
    var sum = directions.routes[0].legs.map(function (leg) {
      return leg.duration.value;
    }).reduce(function (sum, leg) {
      return sum + leg;
    });
    return sum;
  } else {
    return null;
  }
}

/**
 * Calculates the time it takes to travel between two locations.
 *
 * @param {(string|range)} start The start address.
 * @param {string} end The end address.
 * @return {string} The driving time.
 * @customfunction
 */
function drivingTime(start, end) {
  // Handle range in start.
  if (start.map) {
    return start.map(function (s) { return drivingTime(s, end); });
  }
  var startWorkDay = new Date(2016, 5, 23, 9, 30);
  var cache = CacheService.getDocumentCache();
  var key = hash(start, end, startWorkDay);
  var val = cache.get(key);
  // Clean up bad data.
  if (isNaN(val)) {
    cache.remove(key);
    val = null;
  }
  // Cache miss.
  if (val === null) {
    val = Safe.getDrivingTime(start, end, startWorkDay);
    if (!isNaN(val) && typeof val == "number") {
      cache.put(key, val);
    } else {
      return "Not found";
    }
  }
  return Math.ceil(val / 60) + "m";
}