For finer resolution you could try select rbits,wbits,ebits,timeout, though I don't think this is what you are really after.

select(undef,undef,undef, $start - time());
#...4962.38324
#...4963.39886
#...4964.41448
[download]

If you just plug in your calculated difference that gets closer. But again, I don't think thats really what you are after.

select(undef,undef,undef, 0.9993);
#output
#....5554.40476
#....5555.40476
#....5556.40476
[download]

I was wondering if there was a solution that could be derived from using the complements of the numbers, as I have recently been looking at these. I got as close as 0.00129 difference from a second, on the first iteration. Whether its truly to spec, or could be refined, I am not sure, though it looks like something might be there.