Heroku Changelog Heroku Scheduler classified as "best-effort" service

Change effective on 29 April 2013

Heroku Scheduler is being defined as a “best effort” service, meaning that execution is expected but not guaranteed. If scheduled jobs are a critical component of your production application, it is recommended to run a custom clock process instead for more reliability, control, and visibility.

Heroku Scheduler is an add-on for running jobs on your app at scheduled time intervals.