Unlock Posts Over Time

Could be done, but would require a lot of coding.

Maybe look at a paid plugin such as

https://www.premiumwp.com/online-course-learning-management-system-plugin-for-wordpress-sensei/

I found out that this can be done using a feature called “drip feed”. I don’t know much about this. If anyone knows of a free plugin to accomplish this, let me know.

a simple google of drip feed plugin produces

https://www.dripfeedmanager.com/

However from the brief description this just makes a entry visible to all members or not – a feature that is easy to achieve with changing the post date. Anyway hope you can make it work

Paid Memberships Pro has dripfeed and email capabilities – you can download the fully-functional plugin for free – support though does cost money.

@chrisgagner,
I do not know whether your hunt for a drip-feeding plugin has been successful or not, but the plugin at DripFeedManager.com will do your job perfectly. If you are still looking, reach out to me and I will let you have complimentary copy in return for an appraisal.
@Robin W
Thank you for the mention of DripFeedManager’s existence. Your description however is sincerely lacking in an ability to read the description on the site, as it actually states that

This plugin will only display posts to logged in readers who have been members for the specific time the post is protected for

There is absolutely no way that just changing the post date will do that!