You probably want to make a range query, for example, all items created after a given date:
db.gpsdatas.find({"createdAt" : { $gte : new ISODate("2012-01-12T20:15:31Z") }});
I'm using $gte
(greater than or equals), because this is often used for date-only queries, where the time component is 00:00:00.
If you really want to find a date that equals another date, the syntax would be
db.gpsdatas.find({"createdAt" : new ISODate("2012-01-12T20:15:31Z") });