Tested and working. Not sure why people are still trying to use the nightdev api.
Code:
on *:TEXT:!uptime*:#: {
  var %json = streamuptime, %stream = $iif(#* iswm $iif($2,$2,#), $mid($v2, 2-), $v2), %time
  jsonopen -ud %json https://api.twitch.tv/kraken/streams?channel= $+ $lower(%stream)
  if ($JSONError) {
    msg # Unable to retrieve the state of %stream
  }
  elseif ($JSON(%json, streams, 0, created_at)) {
    %time = $ctime($remove($replace($v1,T,$chr(32)),Z))
    msg # %stream has been online for $duration($calc($gmt - %time))
  }
  else {
    msg # %stream is currently not online.
  }
}