Joost is correct, it does mean micro seconds.
Here is the timestr sub in Benchmark::Timer that creates the string... 
sub timestr {
    my $sec = shift;
    my $retstr;
    if($sec >= 1_000) {
        $retstr = commify(int $sec) . 's';
    } elsif($sec >= 1) {
        $retstr = sprintf $sec == int $sec ? '%ds' : '%0.3fs', $sec;
    } elsif($sec >= 0.001) {
        my $ms = $sec * 1_000;
        $retstr = sprintf $ms == int $ms ? '%dms' : '%0.3fms', $ms;
    } elsif($sec >= 0.000001) {
        $retstr = sprintf '%dus', $sec * 1_000_000;
    } else {
        # I'll have whatever real-time OS she's having
        $retstr = $sec . 's';
    }
    $retstr;
}

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In reply to Re: Benchmark Timer explanations by mifflin
in thread Benchmark Timer explanations by Anonymous Monk

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