You can defer indexing and optimisation and let a pair of crons do the jobs.... http://doc.ez.no/Extensions/eZ-Publish-extensions/eZ-Find/2.3/Basic-Configuration/Indexing-content
that's probabaly because delayed indexing is turned off for your eZ Publish site, which is a default behaviour.
Delayed indexing means that objects will not be published immediatelly after publishing, but will be indexed only by running reindexing script from command line.
You can turn on delayed indexing in site.ini / [SearchSettings] / DelayedIndexing=enabled and then set up a cronjob as follows to run at desired times:
