my $start=time;
# ... long processing job goes here...
my $dur = time - $start;

# Print out in appropriate format:
print "Job took $dur seconds\n";

# For longer jobs, I often use one of:
printf "Job took %5.2 minutes\n", $dur/60.0;
printf "Job took %5.2 hours\n", $dur/(60*60.0);
printf "Job took %5.2 days\n", $dur/(24*60*60.0);
printf "Job took %5.2 weeks\n", $dur/(7*24*60*60.0);
# etc.