When you say 'physical store', do you mean a general physical store, or a Lego store specifically? I don't think general physical stores have been following the same street date limits, and I wouldn't expect distribution to be that widespread (and indications suggest that this is going to be a popular product). I don't know if physical Lego Stores *are* holding out for the formal launch date, but if they are, you should have a decent shot there.
However, Online should be easier still, and may go live on midnight; indeed, I suspect you'd be able to attempt to get it online on Wednesday night, and if you're unsuccessful, look into a physical store on Thursday.