The real consideration here isn't any fixed or specific measurement. It's how the bike rides.
If it steers true, with no sense of pulling to either side, than the fork and wheel are fine, even if the the wheel is much closer to one blade than the other.
Otherwise, I'd venture that a reasonable working tolerance for the top of a wheel centering in the top of the fork is probably closer to 2mm TIR (or, 1mm off from the center). If this is a new fork, and you haven't installed it yet, and so can't speak to how it rides, I'd return it. Otherwise, how it rides is trumps.
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