Use millis() in combination with modulo to check every x seconds. In the example below it checks every 10 seconds.

1. void draw() {
2.   if (millis() % 10000 == 0) {
3.     // check for updates
4.   }
5. }

You could also do exactly the same with frameCount to check every 1000th frame for example.

Perhaps you already have them, but let me just mention that threads are important here to keep things running smoothly.

Thanks a lot! I don't know how could I skip that from the docu.

I'd also suggest you take a look at  this article on using Threads for updating data. If you're updating at regular intervals from inside draw(), the animation framerate may fall and there can be visible lag, if the update routine is time consuming. Performing the update in a separate thread is the right way to go in such a scenario.