I could not find an option in the Moodle admin screens for $CFG->forum_enabledtimedposts, either in the forum global settings or by searching the main admin interface.

Did I miss something or is this absent? If it's absent is that on purpose i.e. because there's something wrong with the feature? Maybe it should be placed in 'experimental' if so... (There do seem to be some problems with it and I am going to recommend that we disable the feature here although I don't know how well that will go down...!)