I think a lot of writers tend to do this when writing different cultures, more specifically alien culture. One can't write a book in a alien language because no one would understand it. And if you write the work in English with a bunch of foreign words, readers will still feel like they don't understand what's going on. So a lot of writers tend "translate" the language to English so readers can understand and relate to it, while throwing in a few foreign words in order to make the setting feel like it actually could be a different place/culture.
Now I guess the reason why xats was used instead of minutes was because as you wrote, minutes is a human measurement and the writer may have thought that it wouldn't have made sense for an alien culture to use human time measurements (even though English is a human invention), or maybe thought it would be a neat/good idea to distinguish their culture from ours by giving them their own way of measuring time.