Please note that even though the example shown here appears to have unix timestamps as key_info (Also the same times for apcu_cache_info), this is not guaranteed, version changes (Notably, exactly v5.1.22 uses an internal monotonic clock by default) and configuration options (apc.use_request_time) can make this unreliable.
If, for example, u need to gauge the time distance between now and a key's expiration time without probing the version or functionalities, something like this could be a decent workaround:
<?php
apcu_store('__clock__', 1, 1);
$now = apcu_key_info('__clock__')['creation_time'];
?>