src/Web/Sessions/CachedSessionHandler.php
protected function extractTimestamp($record = []) {
        return isset($record[$this->timestampKey]) ? $record[$this->timestampKey] : null;
    }
protected function extractTimestamp($record = []) {
        return isset($record[$this->timestampKey]) ? $record[$this->timestampKey] : null;
    }
Extract session timestamp from record
@param array $record
@return integer|null