Getting MongoDb document to expire at a certain time using mongoose

Question

I am building an application which allows users to create events at a certain time within a 24 hour period and have the event populate on a google map. While I can get the dates to show up and format properly, my new issue is getting them to expire setting a TTL in each document created.

Here is my mongoose schema:

var mongoose = require("mongoose");
var Schema = mongoose.Schema;

var SportSchema = new Schema({
    title: {
        type: String
    },
    sport: {
        type: String
    },
    location: {
        type: String
    },
    time: {
        type: String
    },
    lat: {
        type: Number
    },
    lng: {
        type: Number
    },
    expireAt: {
        type: Date
    }
});

var Sport = mongoose.model("Sport", SportSchema);

module.exports = Sport;`

and the POST route in my server:

app.post("/api/events", function (req, res) {
  Helpers.geoLocate(req.body.location)
    .then(function (results) {
      Sport.create({
        title: req.body.title,
        sport: req.body.sport,
        location: req.body.location,
        time: req.body.time,
        lat: results.lat,
        lng: results.lng,
        expireAt: req.body.time
      }).then(obj=>res.json(obj));
    });
});

Where the expireAt property gets the same time value at the time property. There are examples out there that are passing a certain amount of time until the record deletes. However, I was trying to see if it is at all possible to pass in a BSON date and have it expire when that data/time is met.