Request the days off now.
I was able to get 8 days off. I put the request in for all 8 days about 4 months in advance and got them all approved. Usually if it's a month or so before hand your chances are better. 9 times out of 10 it will get denied if you're as close as a week in advance. As soon as you know the dates (which it appears you do) put the request in immediately.
ETA: If you only have 4 days, I'm assuming your chances are fairly good. It all depends on how many people have also requested those dates.