Sometimes i meditated some 6 hours a day, in a similar fashion and for a few months with little to show for it.

The issue was that i were meditating during the day and later attacking my exgf or whatnot.

Meditation became something i do to pass the time and i wasn't properly bent on renunciation. 

I guess my suggestion is to look at how you spend your days in general and if possible talk yourself into a wholehearted commitment to the training.

I've experimented with walking & sitting for a long time & a short time. 

Ironically i got nirodha when i was generally struggling, like occasionally crying feeling sorry for myself and not expecting anything special anytime soon. The day of attainment, prior to meditating, i was talking to a monk friend and literally saying that it was too difficult to keep pushing and how i couldn't see myself maintaining the effort lest i broke through something soon.

Was then working 4-6 hours from home, trying to get 1-3 hours in walking/sitting total and at a time when it was fairly difficult to keep all the higher precepts but it worked out as i was otherwise very focused & staying alone.