Thanks, I did not know that.

use strict;
use warnings;

print("Get time1\n");
my $time1 = time();

BEGIN {
   print("Override\n");
   no warnings qw(redefine);
   *CORE::GLOBAL::time = sub { 4 };
}

print("Get time2\n");
my $time2 = time();

print($time1, "\n");
print($time2, "\n");
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Override
Get time1
Get time2
1238164958
4
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