Current Perl documentation can be found at perldoc.perl.org.
Here is our local, out-dated (pre-5.6) version:
If you want finer granularity than the 1 second that the
sleep() function provides, the easiest way is to use the
select() function as documented in
select. If your system has itimers and
syscall() support, you can
check out the old example in http://www.perl.com/CPAN/doc/misc/ancient/tutorial/eg/itimers.pl