$ ./mongo
MongoDB shell version: 2.5.1-pre-
connecting to: test
> db.test.insert({"d":ISODate()})
> db.test.find()
{ "_id" : ObjectId("51db91d2d8e6bfa42833443d"), "d" : ISODate("2013-07-09T04:30:10.144Z") }
> exit
bye
$ ./mongoexport --csv --fields d -d test -c test -o test.csv
connected to: 127.0.0.1
exported 1 records
$ ./mongoimport --type csv -c test -d test --headerline test.csv
connected to: 127.0.0.1
Tue Jul  9 00:30:37.219 imported 1 objects
$ ./mongo
MongoDB shell version: 2.5.1-pre-
connecting to: test
> db.test.find()
{ "_id" : ObjectId("51db91d2d8e6bfa42833443d"), "d" : ISODate("2013-07-09T04:30:10.144Z") }
{ "_id" : ObjectId("51db91ed140f5f1801700482"), "d" : "2013-07-09T04:30:10Z" }
>