Like all coding projects, side projects must be approached at night.

Moonlighting is viewed down upon, and for good reason.

If you have so much energy during the night, it means that you're not giving it 100% during the day.

If you're fine with it, the employer is fine with it, then fuck it.
But otherwise you're being dishonest to the employer and to yourself.
You could be making much more as an employer, or you could just negotiate fewer working hours at 100% efficiency, to spend the rest on your pet projects, and on sleep, which everyone needs.

@AndSoWeCode I feel like your shaming OP based on no context what so ever.

@iSwimInTheC this looks a lot like moonlighting. And the term "side projects" kinda show this as well.

@AndSoWeCode I'd agree if I worked as a software developer. Think of the case where le me does not develop during the day. Well, I kinda have to "moonlight" then, don't I? :$

^ And here's where the context is.

@iSwimInTheC there is an "if" in my original statement. If everyone's fine with it then it's all fine.
Otherwise it really doesn't matter what the day job is, as long as you're not performing it to 100% because you've been debugging code during the night.