This is the date and time in ISO8601 format. "T" separates the date from time, and "Z" indicates that the date is UTC (GMT). MongoDB does not support the Date (only) type, instead everything is converted to a timestamp.
You can go into the mongo console and run a query by which you will see the date (and time) fields that are stored as ISODate ("2011-05-12T13: 51: 33Z").
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