Harvest Time? Should I give it a dark period first?

So,

One of the girls definately looks ready to harvest, the buds could probably swell a bit more but its allready about 5-10% amber under a 30x scope. I think I prefer less couchlock so this girl is ready to go. However, tonight the girls are just about to finish their day period. Can I harvest now, which is the end of their day period or should I wait untill they have been given another 12 hours of darkness?

Apparently they get more THC built up at night, and have less during they day. I don't know if this makes an appreciable difference in potency though.

Won't make a lick of difference but won't hurt either.