So ...

We are going to use a handy plugin called Expire Passwords.

Here it is:

https://wordpress.org/plugins/expire-passwords/

Note: you'll see the usual warning message saying that the plugin hasn’t been tested with the latest major releases of Wordpress ... Ignore it ... I've tested the plugin on Wordpress 5.2 and works fine.

It's a very small plugin (24 KB), but let's see the usual speed tests ...

Here are my results before installing the plugin ...

... and the result after installing and activating the plugin:

No more comments needed ...

Now let's see how it works ...