Does std::condition_variable::wait_until have any advantage against std::this_thread::sleep_for?

As pointed out in the comments already, it depends only on your usecase. The main difference between the two is, that condition_variable can wake up earlier if you trigger it. You also can add a predicate that must be satisfied in order to actually wake up, but that's only a quality of life addition. And btw, the equivalent to sleep_for is wait_for and not wait_until. condition_variable is also great to communicate or synchronize between multiple threads.

Given everything you said, I would use condition_variable for the following reasons:

1. Putting a thread to sleep for longer periods of time is not a good idea because your application can exit at any time (or rather can be requested to exit). In that case you probably want your thread to exit properly, so you have to be able to wake it up at any time.
2. You want to change the config on the fly. If your thread has to restart with new parameters or if you need that thread to actually load the config file you also don't want to wait for the next 20min intervall to end.