Is it possible to schedule plugin updates?

No, but that’s a lovely feature request.

I tried using WP-Cron Events to set wp_update_plugins, wp_update_themes & wp_version_check to only occur Daily at night – but the plugins still trigger updates outside of that time.

This could be the nature of cron. You can say set the time to midnight, but if the cron isn’t triggered until 1am, that’s when the cron will run.

A solution to get things more exact is to set up a crontab. Here’s an example here: https://www.siteground.com/tutorials/wordpress/setup-cron-job.htm

Here’s a more advanced tutorial: https://easyengine.io/tutorials/wordpress/wp-cron-crontab/