Database
[{"date":ISODate("2014-01-01T08:15:39.736Z")},{"date":ISODate("2014-01-01T00:00:00.736Z")},{"date":ISODate("2014-01-01T08:15:39.736Z")},{"date":ISODate("2014-01-01T08:15:39.736Z")}]
Query
db.collection.aggregate([{"$addFields":{"dateStrMatched":{$regexMatch:{input:{"$dateToString":{"date":"$date"}},regex:"00:00:00."}}}},{"$match":{dateStrMatched:true}}])