I don’t think there’s a clear cutoff from a taste perspective, it’ll just be staler the longer you wait. As with most things, it’s just about juggling the convenience vs quality tradeoff. But the win-win solution, especially in the later days, might be that condensed milk everyone’s talking about.
Zelensky has said he understands Ukraine can’t join NATO until the war is over. I think your hypothetical is the reason they wouldn’t be able join in the first place unless they’re in peacetime.