AIUI SD-JSON sends all times as "datetime" in ISO8601 'combined' format, normalised to UTC.
e.g.
"datetime": "2015-07-15T18:30:00Z"
Generally speaking, any program using this datum will want to either (i) select programmes using a date/time range and/or (ii) display the time in local format (+ local TZ). To achieve either of these, the program will probably initially convert the "datetime" to epoch-seconds before performing range checking and/or re-converting for output.
I suggest it would simplify matters for programs using the SD-JSON feed if that feed also included the time in epoch-seconds.
e.g.
"datetime":"2015-07-15T18:30:00Z"
"unixtime":1468607400
If stored in SD database, this has the advantage that the conversion need only be done once (in SD) rather than every time a program accesses the data item (think multiple users independently running the same program on the same data). Two benefits would accrue: faster processing time in the using program, and less chance of conversion error (when a standard library is not used).
Geoff