Database
[{"_id":ObjectId("5fb1828a6dbd2e5c533e2378"),"email":"hskasd@gmail.com","fname":"JOSE","appt":[{"date":"12/04/2020","time":"0900"},{"date":"12/05/2020","time":"1000"},{"date":"12/04/2020","time":"1000"},{"date":"12/04/2020","time":"1000"}]}]
Query
db.collection.aggregate([{$match:{"appt.date":"12/04/2020"}},{$unwind:"$appt"},{$match:{"appt.date":"12/04/2020"}},{$group:{_id:null,time:{$addToSet:"$appt.time"}}},{$project:{_id:0,time:1,count:{$size:"$time"}}}])