use Time::HiRes qw(gettimeofday tv_interval);
my $TH = [gettimeofday];
sub report {
    print $_[0],': ',tv_interval($TH),"\n";
    $TH = [gettimeofday];
}
A: {
  ...do things...
}
report("A");
B: {
  ...do some other stuff...
}
report("B");
C: {
  ...why not more stuff here...
  ...and some more!...
}
report("C");

##</code><code>##

my %TH;
sub report {
    $TH{$_[0]} += tv_interval($TH);
    $TH = [gettimeofday];
}
...
print "$_: $TH{$_}\n" for keys %TH;