My memory is fuzzy. Depending on interrupt latency, you should be able to get within 50ns to 10us of the PPS period. You'd need to check the PPS offset reported by the receiver to see how closely the PPS is aligned with the actual GPS second edge. When I was playing with this a few months ago, I found chrony to have fairly detailed stats of PPS quality including jitter, etc. Tracking down delays in the PPS path can be really tricky so getting absolute accuracy against GPS is hard.
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