It's mostly unimportant and probably not worth studying for. There is software on ETS's site that you can download to take two practice tests that are the exact same format and interface as the real test. My advice would be to take one of these to get accustomed to the style and pace of questions. If you expect a 900+ PGRE, you should ace the quant portion without much effort. I didn't find the verbal section difficult, but I usually score well on the verbal portion of standardized tests (SAT, ACT, etc). The practice tests are also scored, so if you are happy with your first scores, then definitely don't waste any time studying.
Moreover, I think most applicants at top 20 physics schools score very high on the quantitative part (95%+) and it's not uncommon to score fairly high on the verbal part, so it's not a very good way to choose between applicants. I think even a mediocre verbal score isn't really a point against you. If you do poorly on the quantitative section (< 80%?), this might raise a few eyebrows since this is essentially testing high school (or lower) level math. But I doubt even this would hold back an otherwise strong to very strong application.