is it correct to use strtotime() to compare dates?

I have some problems with the following:

<?php
echo "an issue by the function strtotime"."<br />";
echo "01-30-2011 ======".strtotime(01-30-2011)."<br />";
echo "01/30/2011 ======".strtotime(01/30/2011)."<br />";
echo "07-01-2011 ======".strtotime(07-01-2011)."<br />";
echo "07/01/2011 ======".strtotime(07/01/2011)
?>

The result is an issue by the function strtotime:

01-30-2011 ======1310059868
01/30/2011 ======
07-01-2011 ======1310057768
07/01/2011 ======

1. Whi开发者_开发知识库ch format is right to give argument to the function strtotime()?
2. Why is the epoch value changing during the page refresh, even though the argument isn't changed?

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The problem is that you aren't giving strtotime() strings! Put quotes around those parameters first.

echo "01-30-2011 ======".strtotime('01-30-2011')."<br />";
echo "01/30/2011 ======".strtotime('01/30/2011')."<br />";
echo "07-01-2011 ======".strtotime('07-01-2011')."<br />";
echo "07/01/2011 ======".strtotime('07/01/2011')