Weird behavior with process.hrtime()

If I execute this code:

//brute force
console.log('------------------');
console.log('Brute Force Method');
console.log('------------------');
var aTimer = process.hrtime();
var sum = 0;
for (var x = 3 ; x < 1000 ; x++) {
  if (x % 3 === 0 || x % 5 === 0) {
    sum += x;
  }
}
console.log('The sum of them is: '+ sum);
//console.log(aTimer);
var aTimerDiff = process.hrtime(aTimer);
console.log('Benchmark took %d nanoseconds.', aTimerDiff[0] * 1e9 + aTimerDiff[1]);

//arithmetic method
console.log('------------------');
console.log('Arithmetic Method');
console.log('------------------');
var bTimer = process.hrtime();
var term3 = parseInt(999/3);
var threes = 3 * term3 * (term3 + 1) / 2;
var term5 = parseInt(999/5);
var fives = 5 * term5 * (term5 + 1) / 2;
var term15 = parseInt(999/15);
var fifteens = 15 * term15 * (term15 + 1) / 2;
console.log('The sum of them is: '+ (threes + fives - fifteens));
//console.log(bTimer);
var bTimerDiff = process.hrtime(bTimer);
console.log('Benchmark took %d nanoseconds.', bTimerDiff[0] * 1e9 + bTimerDiff[1]);

console.log('------------------');
console.log('Which is Faster');
console.log('------------------');
if (bTimerNano > aTimerNano) {
  console.log('A is %d nanoseconds faster than B.', bTimerNano - aTimerNano)
}
else {
  console.log('B is %d nanoseconds faster than A.', aTimerNano - bTimerNano)
}

The result is:

------------------
Brute Force Method
------------------
The sum of them is: 233168
Benchmark took 64539 nanoseconds.
------------------
Arithmetic Method
------------------
The sum of them is: 233168
Benchmark took 155719 nanoseconds.
------------------
Which is Faster
------------------
A is 91180 nanoseconds faster than B.

That can't be right... arithmetic should be faster. So I uncomment these lines to get a look:

console.log(aTimer);
console.log(bTimer);

And the results look accurate now.

------------------
Brute Force Method
------------------
The sum of them is: 233168
[ 1697962, 721676140 ]
Benchmark took 1642444 nanoseconds.
------------------
Arithmetic Method
------------------
The sum of them is: 233168
[ 1697962, 723573374 ]
Benchmark took 284646 nanoseconds.
------------------
Which is Faster
------------------
B is 1357798 nanoseconds faster than A.

Then I comment those lines out again and I get the same funky results.

What could cause this to happen? Am I missing something about process.hrtime()?

$ node -v
v0.10.0

Edit: I just tested this with v0.8.11 and get the same kind of behavior.