I've learnt meditation is not about emptying the mind, which is impossible, but about interrupting thoughts. You use some "anchor" such as respiration, body sensations, and sounds to reduce the speed of internal talk.
What for?
To reduce anxiety by being more presente in reality, thoughts being virtual and taking us to the past or to the future.
It's a very useful tool during this moment of frustration and expectation, when you might embark in ideas which will cause terrible emotions.
It's also a moment we can't go out and distract from worry or fear, moreover we can't act to change our situation, having simply to accept it, which is a difficult exercise. If we resist it, we'l suffer more.
So, I was told by my meditation coach, to pay attention every time I wish to be anywhere else but where I am - that's called "resistance" in psychology - and gently "como back". You have to insist because our trend is to remeber or project better times, being exposed to frustration.
The presente moment may not be pleasant, but it's what you have and, if you really pay attention, it's not absolutely terrible.