widget cache and settings info pls?

I am a very basic level WP user, so my jargon and questions will be odd.
I am trying your plugin on a small, but heavily integrated (I hope), MultiSite network.

A couple of questions:
1.) In the Settings – what does this mean, and why is the default time so short?:

Cache Expire Time (sec):

My content doesn’t change that often.

2.) Is the caching your plugin does like site-caching-plugins? I would think not. (I already activated it.)
I understand what a site caching plugin does. I never use them. I have a lot of plugins. I have too many potential plugin conflicts.
(And I have noted that when things go bad caching plugins are blamed first, and are warned about in many plugin descriptions. And they are great too. Not for me.)

Thank you

https://www.ads-software.com/plugins/diamond-multisite-widgets/