Seems that war declaration means canceling rights and power of Central Bank in the coutry that declared war.
At least in Russian laws, the power to govern all country finances and reserves goes to wartime administration and Central Bank powers become obsolete.
I didn't check all other countries laws yet, but I suppose they are not very different in the financial part. If you are interested in that rabbit hole - check that thing in the laws of your country. It could be interesting.
If you have examples that disprove that theory, you are welcome too.
Do you know, that most countries don't have such thing as "Congress" at all and have different laws about when and how wartime law could be established?
Also, a question of relationships of Central Bank and wartime administration is independent on the process of declaring war or wartime.