You're misunderstanding. use happens at compile time. Consider:

#file: /perl/site/lib/Foo.pm
package Foo;

use strict;
use warnings;

sub bar
{
    return "BAR";
}

1;

#file: test.pl
use strict;
use warnings;

my $i = 0;

if ( $i )
{
    use Foo;
}
   
print Foo::bar; #prints "BAR"
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