Try taking the print out of the loop. I tried this:

$ perl -wle'use Time::HiRes "time"; my $start = time; while (10000 > k
+eys %t) {
 ++$t{time()-$start} } print "total time ", time()-$start; use List::U
+til "sum"
; print "avg iterations per reported time ", sum(values %t)/keys(%t)'
total time 11.0990000963211
avg iterations per reported time 20.3936
[download]

on cygwin/Windows XP Pro.