Depending on what you are watching in API endpoint, you could use PubSub. For now, it’s only for a few functionalities, but i’m sure it will be extended soon.
Otherwise, API calls each X seconds is still the best solution, maybe try to reuse vars and empty memory once object are done being used between two call intervals. I’d suggest you to do a bit more than 5 seconds, as you have to respect your API rates. If it’s only one endpoint that you reach, there is no problem, but as soon as you’ll have multiple endpoints or same endpoint but multiple users or variant attributes inside the endpoint, it will easily reach it.
Have a great day!