Using the Olark api you can send your visitors a response if your agent does not reply to a message right away.

This script will automatically send a message to your visitor within 45 seconds of the agent not responding. Note that this script will only send a message to the visitor if the agent has never responded to them.

(function() {

  var secondsUntilAutoDelay = 45;
  var didSendMessageToVisitor = sessionStorage.getItem('didSendMessageToVisitor');

  olark('api.chat.onMessageToVisitor', function() {
    didSendMessageToVisitor = true;
    sessionStorage.setItem('didSendMessageToVisitor', true);
  });

  olark('api.rules.defineRule', {

    id: 'delayed_response',
    description: 'Will send a response to the visitor after an agent doesn\'t respond.',

    condition: function(pass) {
      olark('api.visitor.getDetails', function(details) {

        if (details.isConversing &&
            !didSendMessageToVisitor &&
            details.secondsSinceLastMessageToOperator >= secondsUntilAutoDelay) {
          pass();
        }

      });
    },

    // Message the visitor, but also notify the agent that they
    // hit this delay limit.
    action: function() {
      olark('api.chat.sendMessageToVisitor', {
        body: 'Sorry about the delay, I\'m a bit busy at the moment. Be with you in just a moment.'
      });
      olark('api.chat.sendNotificationToOperator', {
        body: 'Automated delay message has been sent to visitor.'
      });
    },

    // Only do this once per visit.
    perVisit: true

  });

})();