The first half of “Ben Is Back” is stronger than the second half, but Julia Roberts and Lucas Hedges hold the movie together throughout. Writer-director Peter Hedges’ film about a 19-year-old drug addict who comes home from rehab for 24 hours to visit his family for Christmas begins as a compelling character study. But then it morphs into a contrived, ticking-clock crime thriller. Still, Hedges — Lucas’ dad — knows well enough to stand back and let his actors act. My review, at RogerEbert.com.