[{"_id":"61179c8d43400f31df195223","name":"song1","time":2000},{"_id":"61179c8341f00f31df159223","name":"song2","time":"00:34:16"},{"_id":"61179c8341f00f31df195223","name":"song3","time":2800},{"_id":"61179c8380f00f31df195223","name":"song4","time":"00:01:10"},{"_id":"61179c8310f00f31df195223","name":"song5","time":"00:15:10"}]

db.collection.aggregate([{$addFields:{time:{$cond:[{$isNumber:"$time"},"$time",{$let:{vars:{time:{$split:["$time",":"]}},in:{$sum:[{$multiply:[{$toInt:{$arrayElemAt:["$$time",0]}},3600]},{$multiply:[{$toInt:{$arrayElemAt:["$$time",1]}},60]},{$toInt:{$arrayElemAt:["$$time",2]}}]}}}]}}},{$sort:{time:-1}},{$limit:1}])