Can I release a squirrel into the wild during winter?

Squirrels do not hibernate. At least in Michigan.

I wouldn't do it since, it seems like most squirrels spend 88% of the summer gathering/hiding acorns.

I think squirrels need acorns to survive the winter.

Therefore, I am predicting that a squirrel without stores of acorns will starve to death.

You don't want to be a baby killer...ahem, a baby squirrel killer that is.

You could try releasing it. It is at a disadvantage and could easily become prey for a dog or hawk.

I'd put whatever he has been caged in outside somewheres safe and sheltered. Food available somewhere else in the yard. He has no fear of you, so as soon as he seems to be on his way to being on his own, you wight want to terrorize it a bit to instill a healthy respect for the evil that can lurk within the hearts of men.

How do you expect your squirrel to fit in with what other squirrels have been doing so long if you domesticated it? Wait until you see other squirrels around too.