The next day? OK, they're responsible.

A week later, they have no responsibility left. Security holes happen, even in "highly secure" systems, because of how complex they are and how difficult it is to harden every possible edge case. But people not knowing the hole exists when you find and patch it isn't really possible, which is why they give advisories that "this is serious, you need to install it" in the first place. Every day after the patch is shipped increases your risk that bad actors have used the new knowledge to find a way to exploit the vulnerability, not through any failure of the vendor, but by the nature of what security is.

A hole existing isn't negligent. Leaving a known vulnerability, with a shipped fix, unpatched for a week on platforms that hold sensitive consumer information is. And it's a decent ways up the severity scale of negligence, too.