Dynamic content in template

This sounds like page caching. Page caching is a good thing, it keeps your site fast. The downside is that any personalized data is not accurate, which is why the clock is not updated.

It looks like perhaps WPEngine doesn’t give you control over page caching – https://wpengine.com/blog/no-caching-plugins/

You may need to speak to them about a workaround for this. However, in my experience, it might be a hard sell.

Can I ask why this needs to be done in PHP? It seems to me that the performance tradeoff is not worth the gain.