The source of these warnings is that both POSIX and Date::Format happen to export the same subroutine names into the main:: namespace by default, such as sub strftime: 
$ perl
use strict;
use warnings;
no warnings "all";
use Test::More tests => 2;

BEGIN { use_ok('POSIX',        'strftime'); }
BEGIN { use_ok('Date::Format', 'strftime'); }
__END__
1..2
ok 1 - use POSIX;
Prototype mismatch: sub main::strftime: none vs ($\@;$) at /usr/lib/pe
+rl5/5.8.5/Exporter.pm line 65.
 at (eval 4) line 2
ok 2 - use Date::Format;
$

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Exporter says
Exports pollute the namespace of the module user. If you must export try to use @EXPORT_OK in preference to @EXPORT and avoid short or common symbol names to reduce the risk of name clashes.
In your case I guess it comes down to selectively exporting only those functions you are going to use, while carefully making sure you don't get any namespace collisions.

I think it is bad practice of Date::Format to export a subroutine name by default that collides with another subroutine name from a package that is included in core perl. A possible patch to Format.pm could be: 

$ diff Format.pm.org Format.pm
15c15
< @EXPORT  = qw(time2str strftime ctime asctime);
---
> @EXPORT_OK  = qw(time2str strftime ctime asctime);

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--
No matter how great and destructive your problems may seem now, remember, you've probably only seen the tip of them. [1]

In reply to Re: Issues when testing module loading by andreas1234567
in thread Issues when testing module loading by skx

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