Use Rate Limit "one per X" per *instance* in a subflow?

I have a subflow that I'm calling twice in one workflow but passing in different environment variables. Within the subflow I've got a section that I'd like to only run once per three hours so I've got a Delay Node with Rate Limit selected. The problem is I want one message to pass through for each subflow instance, but as best I can tell the rate limit is being shared across both instances -- specifically the rate limited section executes for the first subflow but not for the second one.

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Am I misunderstanding what's happening? Is there a way to get this to work so that the rate limit is only per-instance? Is this just the wrong tool for the job?

Thanks in advance!

Each subflow instance should be independent so should act on their own terms.

That's what I thought, which is why I'm confused by the behavior I'm seeing. I guess I'll have to try to debug some more. Thanks