I've been using Nihongo Master on and off for a few years and I've never been able to obtain the achievement where you need to be logged on for a long period of time.
I am quite often finding that the system needs me to relogin often throughout the day, this making this achievement extra difficult to obtain.
I realise it isn't considered healthy or good in anyway to study for so long, but I am a bit of a perfectionist and would like to obtain any achievement I see on the list... speaking of... I also would like to add on that I welcome seeing new achievements added. ;)