Currently it is only possible to search for dates (created and posted). In my application a time based search is required, because a lot of pictures are taken per date.
Currently the time part of a datetime is not parsed. If the time was parsed optionally, it would be possible to query a complete datetime.

https://github.com/Piwigo/Piwigo/blob/bd152ba00e0a26bb9a270e5d7bc924fe42d0aac3/include/functions_search.inc.php#L674C1-L689C6