How do I stay motivated at my day job?

I recently graduated from university (Strike one for many, I am sure) with a STEM degree (...Strike two)

I have an idea that I have been dying and going back to over the past year and I am working on the MVP to prove that it is at the very least viable before I do anything rash. (Don't worry, the MVP hasn't taken a year, I started writing it in early March)

I get paid a decent amount of money at work but I am not fulfilled at work (Not to mention, I feel vaguely underpaid). I am not growing. It is boring. I get up at 7:30, take a shower, work on my project (admittedly not as focused as I should be) until 9:30 then go to work. I get into work and I am already dying to go back at by 12:30. I come home around 7 and work until midnight on the project.

How do I stay motivated at my day job when like every cell of my body just wants to leave and do something different? I know this may be more of a career question than anything but I really honestly don't feel like doing what I am doing anymore.

I love and adore programming... but I don't love having to wait for others so I can write my tiny bit, I don't like having essentially no input on what I am working on. It is a small team at a startup and I know they want me to give input and just go crazy on whatever I want. But I genuinely do not care. I don't care. The product is fucking awesome, I want them to succeed but I deep down do not care either way about things.

To me, work is just a way for me to get money to fund my own projects and to not have to do what I am doing right now.

Maybe I am immature (feel free to say so), maybe I am undisciplined (tell me that too). I just want some insight, encouragement, helpful advice on how I can keep going besides this somewhat ethereal goal of "Someday I'll leave". I have a rough plan of what I need in place before I 'go for it' but obviously things take time. As much as I'd love to walk out and throw caution to the wind, my landlord doesn't take optimism as payment ;)