api json ZOHO_DATE_FORMAT?

api json ZOHO_DATE_FORMAT?

I'm attempting to use the IMPORT function with JSON on the Zoho Reports API but cannot seem to get the ZOHO_DATE_FORMAT right. The standard JSON ISO 8601 date format looks like this:

2014-01-04T12:15:00.000Z

I've tried the following with no luck:
"yyyy-MM-dd'T'HH:mm:ssZ" 

Here's the error response:
{
 "response":{
   "action":"IMPORT",
   "error":{
     "code":8509,
     "message":"The parameter ZOHO_DATE_FORMAT does not match the accepted input pattern"
   }
 }
}

I've also tried without ZOHO_DATE_FORMAT specified and, while it does import the records successfully, it imports the dates as string fields and will not let me convert in the GUI (which is unacceptable as I need to filter based on the dates in our reports).

What is the proper ZOHO_DATE_FORMAT for ISO 8601 dates in JSON?