MongoDB aggregation query that returns summarized Basis sleep data for each day

gistfile1.json

db.sleeps.aggregate( [
	{ $unwind : "$content.activities" },
	{ $project : 
		{
		"content.activities.date" : 1 ,
		"content.activities.sleep" : 1,
		"content.activities.start_time" : 1
		}
	},
	{ "$group": { 
		_id: "$content.activities.date",
		start_time : { $min : "$content.activities.start_time.iso"},
		offset : { $min : "$content.activities.start_time.time_zone.offset" },
		light_minutes : { $sum: "$content.activities.sleep.light_minutes" },
		rem_minutes : { $sum: "$content.activities.sleep.rem_minutes" },
		deep_minutes : { $sum: "$content.activities.sleep.deep_minutes" },
		interruption_minutes : { $sum: "$content.activities.sleep.interruption_minutes" },
		unknown_minutes: { $sum: "$content.activities.sleep.unknown_minutes" }
	 } },
	 { $sort: { _id : 1 } },
	 { $out: "sleepexport" }
])