This article explains working behavior of OSPF overload command with and without timeout option.

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OSPF overload sets the metrics for the overloaded router to the maximum cost, which forces traffic to take other lower-cost paths if they are available.

OSPF overload does allow transit traffic through the overloaded router if it is either the only or the best cost path to reach a destination.

With timeout option:

Overload option works only when router comes online and once timeout value expires all transit traffic starts to flow in this device.

Without timeout option:

Until overload option removed from the configuration, transit traffic does not pass into the device.