start_timestamp

Required. A timestamp representing when the measuring started. The

format is either a string as defined in RFC

3339 or a numeric (integer or float)

value representing the number of seconds that have elapsed since the Unix

epoch. The start_timestamp value must be less than or

equal to the timestamp value, otherwise the Span is discarded as invalid.

{
  "start_timestamp": "2011-05-02T17:41:36.242Z"
}

or:

{
  "start_timestamp": 1304358096.242
}