Time limit cache

Hello awesome community,
I'm trying to speed up my website using the cache system but I'm facing a problem I do not know how to solve. I have a plugin that reads a json file with opening times, opening days, hoilidays bla bla bla and compare them to the actual date:time printing out in a page if the activity is open or closed etc. etc. It works and I'm proud of it.
The problem happens when I active the cache: the page is cached (yeah) but when it tries to print the current date:time it stamps the time when the page was cached, so I lose its utility.
How can I use the cache system and the realtime date:time check? Can i say "hey cache, check me again in xx minutes"?

if your page needs to be dynamic, why dont' you simply turn off the page cache for that one page with a cache_enable: false in the page header? The site will still run fast, but that one page's content will not be cached.

thank you!