Create Time, Last Modified Time we prefer to store in UTC. However, its ALWAYS shown in the user’s timezone while viewing it in browser. While retrieving via API, it will be again based in UTC. Since it has TZ information, your application can adjust based on it.
I tried it using latest NocoDB docker release with PG as root DB – with both DB timezone set to default (UTC) and modified DB timezone (Tokyo/Japan). In both of these instances, the displayed timezone for CreatedAt & UpdatedAt fields matched browser timezone