Database
[{"_id":ObjectId("5eb2bbb3b278b3c384106a20"),"mongodate":ISODate("2020-05-05T19:42:00Z"),"createtime":"1588366164434"},{"_id":ObjectId("5eb2bcabb278b3c384106a21"),"mongodate":ISODate("2020-05-05T19:42:00Z"),"createtime":"1588466164434"}]
Query
db.collection.aggregate([{$project:{epoch:{$toLong:"$mongodate"},createepoch:{$toLong:"$createtime"}}},{$project:{difference:{$subtract:["$epoch","$createepoch"]}}},{$group:{_id:null,min:{$min:"$difference"},max:{$max:"$difference"},avg:{$avg:"$difference"}}}])