You've left the crazy startup and you've joined a new company.
How do you become "normal" again, without feeling like you're under working or not pulling your own weight?
To me, there are two separate dimensions. One is how the individual fits into a different work culture; the other is the work culture fits into the individual's life.
The fitting into the work culture has to happen relatively quickly. Building a life around a work culture can happen over time...maybe there's a second job or a hobby or reading or all of them in varying amounts. Maybe it's another role within the current company or at a different company...eventually, that's almost inevitable.
Good luck.
So, first, remind yourself a normal 40-hour work week is actually the best thing you could be doing for your employer long term. See similar point I made over at http://codewithoutrules.com/2016/02/24/go-home-already/
Second, the biggest benefit you can provide for your employer is coming up with the smart solution that reduces the amount of necessary work by an order of magnitude. And you don't do that by working real hard for a long time. You do that by thinking. And thinking is in part a thing you do in the back of your head while doing other stuff. See Rich Hickey's talk http://www.youtube.com/watch?v=f84n5oFoZBc