From the docs for sleep (with minor reformatting):
For delays of finer granularity, you may use Perl's syscall
interface to access setitimer(2) if your system supports it,
or else see select above. The Time::HiRes module
(from CPAN, and starting from Perl 5.8 part of the standard
distribution) may also help.
Following the reference to select, we find:
You can effect a sleep of 250 milliseconds this way:
select(undef, undef, undef, 0.25);
Note that whether select gets restarted after signals
(say, SIGALRM) is implementation-dependent.
Please try reading the perldocs before asking questions here.