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;
}
