Unfortunately there is no recipe for rapidly re-booting yourself, your motivation or anything about you.
There are some red flags here. The request of your presence in the office, not having a roadmap, missing features / bugs list, etc. What I'd do is to get rid of them asap.
But.. There is zero time to chill-out? There is always time and it is flowing. At this point, it doesn't matter if you sit in front of your computer for 12 hours; it's what you've done on your time. Stop. Take 2-3 days off and tell them to organise in the meanwhile. Tell them about how they are consuming you and when you get back at working you want to do things better.
Go out to the nature on your off time. Go to a swimming pool or swim in the sea if you can, ride bicycle, run, read something you've enjoyed in your childhood. Take the computer out of your sight. Spend time with your family, the ones those make you just happy. The idea here is remembering how it's to be happy and productive. Also some thoughts will occur such as are you doing everything as you should? are you alright with the outcome of the work you've completed so far? etc.
Well actually there is a recipe for getting your motivation back, and TheSmoke has pointed the way.
[1] Take a week-long break from work and do something enjoyable. If you can't take a break, go to step [2].
[2] In the long-term you need to either fix your attitude to your job, or change your job. If it's a contract job, see if you can last until the end of the contract, then take something else.
I suspect you will need to ditch the job. If you do that, make sure you try to take a break before starting the next time, to give yourself time to reboot your motivation.
If you're starting to experience any kind of serious depression or burnout, you really need to quit the job pretty soon before it gets out of hand (I've been there).
Just remember there are always other opportunities out there - you are never as trapped as you think you are.
This helps me to unwind, I actually cycle to work and swim once a week, so far I am in good mental shape, but lack any motivation to work on the project and in that environment.
There are some red flags here. The request of your presence in the office, not having a roadmap, missing features / bugs list, etc. What I'd do is to get rid of them asap.
But.. There is zero time to chill-out? There is always time and it is flowing. At this point, it doesn't matter if you sit in front of your computer for 12 hours; it's what you've done on your time. Stop. Take 2-3 days off and tell them to organise in the meanwhile. Tell them about how they are consuming you and when you get back at working you want to do things better.
Go out to the nature on your off time. Go to a swimming pool or swim in the sea if you can, ride bicycle, run, read something you've enjoyed in your childhood. Take the computer out of your sight. Spend time with your family, the ones those make you just happy. The idea here is remembering how it's to be happy and productive. Also some thoughts will occur such as are you doing everything as you should? are you alright with the outcome of the work you've completed so far? etc.
Good luck with it and hope you can overcome this.