MongoDB Aggregation Pipeline : conditionnal multiplication

how about this? it converts the number to date the multiple 1000 was to convert seconds to milliseconds

db.topic_scorings.aggregate(
   [
      {
         $project:
           {
             status: 1,
             newDateField:
               {
                 //$cond: [ { "$eq": [ "$status", "submitted" ] }, "$updated_at", { $convert : { input: "$updated_at", to: "long" } } ]
                   //$cond: [ { "$eq": [ "$status", "submitted" ] }, "$updated_at", { $toDate : { $convert : { input: "$updated_at", to: "long" } } }]
                   $cond: [ 
                        { "$eq": [ "$status", "submitted" ] }, 
                        "$updated_at", 
                        { $toDate : { $multiply : [ {$convert : { input: "$updated_at", to: "long" } }, 1000 ] } }
                   ]
               }
           }
      }
   ]
)