Database
[{"_id":1,StartTime:1689206300000},{"_id":2,StartTime:1689206400001}]
Query
db.collection.aggregate([{$match:{$expr:{$gte:["$StartTime",{$toLong:{$dateFromString:{dateString:{$substr:[{$toString:"$$NOW"},0,10]},format:"%Y-%m-%d"}}}]}}},{"$addFields":{date:"$$NOW",convertedDate:{$toLong:{$dateFromString:{dateString:{$substr:[{$toString:"$$NOW"},0,10]},format:"%Y-%m-%d"}}}}}])