I thought so, too, but looking at https://www.rio2016.com/en/swimming-sw-mens-1500m-freestyle-..., there were quite a few differences smaller than that in Rio. 38 vs 39 is 0.03 seconds (in different heats, but qualification for further rounds is on time), 3 vs 4 is 0.24 seconds in the same heat.
And I don't see how the race length would be a factor here, as it doesn't affect the relative difference.
It's only at the really short races that the error becomes smaller than the accuracy of the timing.
And I don't see how the race length would be a factor here, as it doesn't affect the relative difference.
It's only at the really short races that the error becomes smaller than the accuracy of the timing.