Time allowed to proc Duskblade is kinda high

I understand that the new damage bonus on duskblade is pretty strong, but I find weirder is that you have 5 seconds after being spotted in order to proc it. It was 4 seconds before the patch, and this change helps pretty much everyone other than assassins. Shouldn't 3 seconds be more than enough for an average assassin to go in, proc duskblade, and execute their combo? Even if I'm playing a mid lane assassin like zed and talon, I'm not really gonna stand in the open for half an hour before going for the kill, not in mid lane, and definitely not if i'm roaming.