Much like DNS, it depends on the TTL. But yeah, if you're trying to do real-time stuff, it's best not to cache that with out-of-the-box stock CDN products, but rather have your own caching. Then for the rest of the endpoints/assets, you can use a default CDN.

Something some people seem to miss though, is to leverage ETag header properly, so the client and CDN can serve fresh content automatically when it exists, or serve the cached content otherwise. It's not that tricky, but somehow many seems to not even know about it.