title: Airflow: changing the crontab time for a DAG in Airflow
body: <p>I have a DAG that has been running everyday at 3:00, it ran OK for the past few weeks. </p>
  
  <p>I've updated the date to run now at 7:00, but apparently for the last 2 days it didn't run. I can see the tasks for those two days with the status 'running' (in green), but no command is triggered. </p>
  
  <p>Does one needs to do something more to change de running time of a DAG ?</p>
  
  <p>I know that in the past one way to solve this was to clean in the meta-database the tasks for this DAG, and update the start_date, but I would rather avoid doing this again.</p>
  
  <p>Anyone has a suggestion?</p>