gistfile1.js

var sendgrid  = require('sendgrid')(api_key);
var moment    = require('moment'); // I use this for time cos it's ace
var userInfo  = require('./test.json'); // for example purposes this would be the JSON you sent me, you would probably be getting this from a DB or via another call...

var email     = new sendgrid.Email({to: userInfo.emailData.email}); // Set up the initial email object, we're sending to Andy.

var timeToSend = moment(userInfo.send_time).unix(); // Scheduled send takes a UNIX timestamp, I used MomentJS to make it
email.setSendAt(timeToSend); // Set the scheduled send time

email.setUniqueArgs({user: userInfo.User}); // Let's pass the username via a unique arg, you'll get this back via the Event Webhook, helps to uniquify tracking
email.addCategory('daily update', 'personalised'); // Additionally, any category you want, this is also kind of like tagging, you'll get this back via Event Webhook, it'll also show in aggregated stats in the SG dashboard

email.subject = "This is a subject"; // Whatever words you want

email.addFilter('templates', 'enable', 1); // Turn on templates for this email
email.addFilter('templates', 'template_id', userInfo.template); // Which template to use

// Set up a loop to do the stories build
for(var i; i < userInfo.Data.length; i++) {
  email.addSubstitution('subheading', userInfo.Data[i].subheading);
  
  for(var s; s < userInfo.Data[i].stories.length; s++){
    email.addSubstitution('url', userInfo.Data[i].stories[s].URL);
    email.addSubstitution('headline', userInfo.Data[i].stories[s].Headline);
    email.addSubstitution('short_story', userInfo.Data[i].stories[s].ShortStory);
  }
  
}

sendgrid.send(email, function(err, json) { console.log(err | json); });