Here is some interesting test code. Lowest difference I could get was 1 microsecond. I certainly wouldn't take this as proof, combining the timestamp with some other info is easy and pretty fool proof.

#!/usr/bin/perl
use Time::HiRes qw(gettimeofday);
my $min = 10;
my $max = 0;
for (0..1_000_000) {
    ($secs1, $micro1) = gettimeofday();
    ($secs2, $micro2) = gettimeofday();
    $diff = (($secs2 * 1_000_000) + $micro2) - (($secs1 * 1_000_000) +
+ $micro1);
    $max = $diff if $diff > $max;
    $min = $diff if $diff < $min;
}
print "Min difference: $min\n";
print "Max difference: $max\n";
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