Time on Page with UDF (User Defined Functions)

SELECT
  fullVisitorId,
  visitId,
  hitNumber,
  pagePath,
  diff AS timeOnPage_ms
FROM
  timePerPage(
  SELECT
    fullVisitorId,
    visitId,
    NEST(hits.page.pagePath) AS pages,
    NEST(hits.type) AS types,
    NEST(hits.time) AS times
  FROM
    [google.com:analytics-bigquery:LondonCycleHelmet.ga_sessions_20130910]
  GROUP BY
    fullVisitorId,
    visitId
  LIMIT
    10)