If you plan to store UUID values in a Primary Key column, then you are better off using a TSID (time-sorted unique identifier).
One such implementation is offered by the Hypersistence TSID OSS library, which provides a 64-bit TSID that’s made of two parts:
a 42-bit time component
a 22-bit random component
The random component has two parts:
a node identifier (0 to 20 bits)
a counter (2 to 22 bits)
The node identifier can be provided by the tsid.node system property when bootstrapping the application:
-Dtsid.node="12"
JSON itself does not specify how dates should be represented, but JavaScript does.
You should use the format emitted by Date's toJSON method:
2012-04-23T18:25:43.511Z
The overhead is due to the SSL handshakes, which are lengthy and drastically increase the number of round-trips required for a HTTPS session over a HTTP one.