What do guests on a show like Meet the Press hear in the earpieces they wear?

Are they being warned that they need to "wrap it up", or ....?
What if the host would like to hear them continue what they are saying.

I assume the main concern is that guests aren't allowed to run long to the point that they can't get their commercials in. Any other reason?

Kini2017-12-24T17:16:53Z

They are told when they are not being biased enough.