Have a close look at the corresponding manual (e.g. opcache.force-restart-timeout
). You can schedule a restart if you want, or simply increase the frequency in which the timestamps are compared. The default behavior of Opcache is to throw out the oldest files and free memory.
If you have performance issues, disable all of these features. Set the TTL to zero, never check the timestamps and only reload your PHP files if you apply an update to the actual PHP files. The cache will be filled once with all your stuff and that's it. Of course the 128 MB should therefore be enough to cache all possible script execution paths. I think a default WordPress installation should easily fit into such a cache, but it might not if you have some extensions (I really don't know).