What is needTime on MongoDB cursor.explain("executionStats")? - mongodb

Question

I was checking that my query is optimum or not. For that I used Cursor.explain("executionStats"). At there few keys present which I am curious to know about.
So I found needTime. I researched on MongoDB Official Documentation but unfortunately, I was not able to understand. Is there anyone who help me out regarding this.
This is my result:
"winningPlan" : {
"stage" : "PROJECTION",
"transformBy" : {
"views" : 0,
},
"inputStage" : {
"stage" : "SORT",
"sortPattern" : {
"createdate" : -1
},
"limitAmount" : 20,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"post_status" : {
"$eq" : 1
}
},
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"user_id" : 1,
"lastmodified" : -1
},
"indexName" : "user_id_1_lastmodified_-1",
"isMultiKey" : true,
"multiKeyPaths" : {
"user_id" : [ ],
"lastmodified" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"user_id" : [
"[MinKey, MaxKey]"
],
"lastmodified" : [
"[MaxKey, MinKey]"
]
}
}
}
}
}
},
"rejectedPlans" : [ ]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 20,
"executionTimeMillis" : 1,
"totalKeysExamined" : 386,
"totalDocsExamined" : 375,
"executionStages" : {
"stage" : "PROJECTION",
"nReturned" : 20,
"executionTimeMillisEstimate" : 0,
"works" : 409,
"advanced" : 20,
"needTime" : 388,
"needYield" : 0,
"saveState" : 3,
"restoreState" : 3,
"isEOF" : 1,
"invalidates" : 0,
"transformBy" : {
"views" : 0,
},
"inputStage" : {
"stage" : "SORT",
"nReturned" : 20,
"executionTimeMillisEstimate" : 0,
"works" : 409,
"advanced" : 20,
"needTime" : 388,
"needYield" : 0,
"saveState" : 3,
"restoreState" : 3,
"isEOF" : 1,
"invalidates" : 0,
"sortPattern" : {
"createdate" : -1
},
"memUsage" : 19348,
"memLimit" : 33554432,
"limitAmount" : 20,
"inputStage" : {
"stage" : "SORT_KEY_GENERATOR",
"nReturned" : 225,
"executionTimeMillisEstimate" : 0,
"works" : 388,
"advanced" : 225,
"needTime" : 162,
"needYield" : 0,
"saveState" : 3,
"restoreState" : 3,
"isEOF" : 1,
"invalidates" : 0,
"inputStage" : {
"stage" : "FETCH",
"filter" : {
"post_status" : {
"$eq" : 1
}
},
"nReturned" : 225,
"executionTimeMillisEstimate" : 0,
"works" : 387,
"advanced" : 225,
"needTime" : 161,
"needYield" : 0,
"saveState" : 3,
"restoreState" : 3,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 375,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 375,
"executionTimeMillisEstimate" : 0,
"works" : 387,
"advanced" : 375,
"needTime" : 11,
"needYield" : 0,
"saveState" : 3,
"restoreState" : 3,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"user_id" : 1,
"lastmodified" : -1
},
"indexName" : "user_id_1_lastmodified_-1",
"isMultiKey" : true,
"multiKeyPaths" : {
"user_id" : [ ],
"lastmodified" : [ ]
},
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"user_id" : [
"[MinKey, MaxKey]"
],
"lastmodified" : [
"[MaxKey, MinKey]"
]
},
"keysExamined" : 386,
"seeks" : 1,
"dupsTested" : 386,
"dupsDropped" : 11,
"seenInvalidated" : 0
}
}
}
}
}
},