I changed from HDMI to DisplayPort and now it wakes much faster - about a second. 
My U2723QE (Rev A02) is slow to turn back on after it powers down due to idleness. It takes about 5 full seconds whereas my old Ultrasharp took 1. My desktop PC never hibernates, I am talking strictly about Window's "Power monitor off after 5 minutes" feature. I am not charging any USB devices and in fact don't have the USB hub connected at all at the moment.
U2723QE, slow to wake?