Statistics are generated each time an API Call is made, per call per location. Aggregated statistics are also generated for the hour, day, week, month and year (all based on UTC).
Example:

{
  "meta": {
    "kind": "MONTH", 
    "call_id": "agxkZXZ-dmlhdGVzdHNyFwsSClRlc3RTZXR1cDIYgICAgKDDxwgM", 
    "type": "ALL", 
    "time": "2015-10-01T00:00:00Z", 
    "location_id": "", 
    "name": "API test name"
  }, 
  "stat": {
    "avg_latency": 383.5, 
    "max_latency": 749, 
    "time": "2015-10-01T00:00:00Z", 
    "count": 20
  }
}

Data available for all results:

Name	Type	Description
time	DateTime	Normalized time for the period requested.
count	Integer	The number of API calls made in the specified period.
max_latency	Integer	The slowest API Call made in the specified period in ms.
avg_latency	Float	The average latency for the API Calls for the specified period.

Extra data is available for results that passed (i.e. when type is set to COMPLETE).

Name	Type	Description
time	DateTime	Normalized time for the period requested.
count	Integer	The number of API Calls made in the specified period.
max_latency	Integer	The slowest API Call made in the specified period in ms.
min_latency	Integer	The fastest API Call made in the specified period in ms.
avg_latency	Float	The average latency for the API Calls for the specified period.
standard_deviation	Float	The standard deviation of API Call latencies for the specified period.
skewness	Float	The skewness of API Call latencies for the specified period.

Data that is available when requesting raw data, i.e. kind = RAW.

Name	Type	Description
time	DateTime	The time that the API Call was made.
latency	Integer	The length of time, in ms, that the API Call took to make.
http_code	Integer	The HTTP response code returned.
content_length	Integer	The size, in bytes, of the response.