Yes use your judgement on when they are mature. You want to wait generally untill all the pistils have turned brown and receeded before you even think about flushing if you decide to. I encourage everyone to try things out themselves, but personally after doing the tests, I don't flush my plants at harvest. I prefer to feed my plants gently so they can finish maturing happily rather then starving them the last 2 weeks.
It generally takes a good 7-20 days for plants to actually begin to flower after you switch your lights. That time depends on the genetics and environment. from that point it will generally take 8-10 weeks for most strains to fully mature. Some sativa dominant strains can take 12+ weeks as has been discussed.
From looking at your pictures and considering what you told me, I would say you are in week 2 of flowering. The plants are about to do some major growth, so keep them healthy and enjoy the show. Don't even think about flushing or anything harvest related for another 7-8 weeks. Once you start to see signs of maturity, and the buds seem to have stopped growing larger THEN your getting close.