Well, this person is aware of having aversion towards someone who's consistently late. Okay, what's that got to do with you? In a sense, are they harming you? If somebody is consistently late, are they actually harming you? If you're in the retreat, the answer would be, "no". The most irritation they possibly will cause for you is possibly a bit of noise at the beginning of a session, and you get upset at a noise.
The other thing I can think of is that it may delay Rosemary or me from starting our talk. As you know, we generally wait until everybody's in the hall. If somebody's late, it means we're delayed. Does that harm you? Either way we look at this, to have aversion towards someone being late is useless, because they're not even harming you.
Now aversion in general, when it's unwise aversion, it's useless, also. Wise aversion is quite okay, i.e. having aversion to people who are murdering, people who are stealing, and so on. Wise aversion is fine, but unwise aversion is actually harming you. So when you're having aversion toward somebody else, you need to bring up much more of the Compassion/Lovingkindness meditation techniques. Much more Compassion/Lovingkindness for ourselves, that we're creating this aversion within ourselves, just from a sight or a sound. Because that's all that's happening.
If, back in the West, there's an important job and things have to be done on time, that's a different story, but the question is regarding the retreat here. How you can deal with aversion in retreat is actually going to help you deal with it out there as well. So, we need Compassion for ourselves, that we're actually creating our own pain.
Compassion for the other person is also helpful. Indeed, someone who's consistently late, whether it's here, or anywhere in the world, they have a problem. A problem with what we would call "time management". So, try to open your heart for somebody who has this sort of problem, and to open your heart for yourself, that you actually get upset with somebody about such a minor thing.