Nice man! Your purps look good, I'd flip em in the next 10 days or so. Depends how branchy you wanna em to get.
I got some purps from BCSK going now about 1/2 way through flower on an 8 week pheno, and a few more that are about 1/3 way through on a 9/10 week pheno. The more indica pheno tends to purple up about 3 weeks into flower and the more sativa pheno tends to go more purple a little later. The sativa pheno drips resin even early in flower, at 3 weeks resin is dripping down to the tips of the bud leaves. The indica pheno stays very squat and bushy, the one I have grows to about 2 feet tall with 8 or more main colas. The sativa pheno seems to grow 1 fat cola with about 4 smaller side colas. I prefer the sativa pheno as it gets me super high but the indica pheno is not shabby by any means.
There are a couple people around that have or regularly have purps from BCSK going. Massproducer had a very nice grow journal of the purps about a year ago, and I have a couple of my purps grows documented in the grow journal section as well.
Did you get any other strains with the purps? The genetics from them are great.