Checklist

• I have included the output of celery -A proj report in the issue.
  (if you are not able to do this, then at least specify the Celery
  version affected).
• I have verified that the issue exists against the master branch of Celery.

> celery report

software -> celery:3.1.25 (Cipater) kombu:3.0.37 py:2.7.12
            billiard:3.3.0.23 py-amqp:1.4.9
platform -> system:Linux arch:64bit, ELF imp:CPython
loader   -> celery.loaders.default.Loader
settings -> transport:amqp results:db+postgresql://username:**@host/db_name

CELERY_TASK_RESULT_EXPIRES: 604800

Steps to reproduce

I set CELERY_TASK_RESULT_EXPIRES to 1 week i.e. 604800 based on the docs so that my task results are persisted for up to 1 week

Expected behavior

Celery beat executes everyday and clears task results older than 1 week

Actual behavior

Celery beat executes everyday and clears task results older than 12 hours