Doesn’t really matter. Do it when a till is up if you can even if you make it before or after you mark it out, if you forget it’s not the end of the world.

Someone would have to assign again once the tills are closed but you can do that without there being a drawer

My store won’t allow us to order drinks if we actually open, we have to wait for our breaks either way. As far as tills we always have to open one too.