Please try using this CVS snapshot:

  http://snaps.php.net/php5-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5-win32-latest.zip

This server does not run php5.  It's on php4

Right. And I didn't ask you to upgrade the server. I asked to to try the latest snapshot.
And I'd really appreciate if you provide a reproduce code without HTML/forms/etc. Just a plain, short and clean PHP code that demonstrates the problem.
Thanks in advance.

Ok I'll see about testing it agains the latest CVS if I have a chance.

A 100% php example is as follows:

<?
$timestr="Friday at 7pm";
print "Starting Value: '$timestr'\n";

for( $x=1; $x<=10; $x++) {
        $timestr=strftime('%A, %B %e %Y at %r',strtotime($timestr));
        print "The string is now: '$timestr'\n";
}
?>

Results of testing on PHP-5.1-dev CVS (php5-200506222230), with various format strings:
==============================================================
<?php
$formats = array (           // CHANGE : RESULT ON PHP-5.1-DEV
        '%A, %B %e %Y at %r',// original: +1 week +12 hours
        '%A %B %e %Y at %r', // remove comma: +1 week +12 hours
        '%A %B %e %Y %r',    // remove 'at': +1 week -2 hours
        '%r %A %B %e %Y',    // move %r to front: +1 week
        '%r %B %e %Y'        // remove the '%A' (day): -2 hours
                 );

foreach ($formats as $format) {
  print "-------- $format -----------\n";
  $timestr="Friday at 7pm";
  print "Starting Value: '$timestr'\n";

  for($x=1; $x<=10; $x++) {
    $tStamp = strtotime($timestr);
    $timestr=strftime($format,$tStamp);
    print "x: $x; timestr: '$timestr'; tStamp: $tStamp\n";
  }
}
?>

Some corrections, updates, relevant information, and then questions for PHP-5.1-dev:
=================================================================
Correction - This line:
        '%r %B %e %Y',       // remove the '%A' (day): -2 hours
Should say this instead:
        '%r %B %e %Y',       // remove the '%A' (day): -14 hours
=================================================================
Using this format string on PHP-5.1-dev leads to no change:
        '%r %B %e %Y %z'     // Add the timezone: No change.
=================================================================
Please see this comment at http://php.net/strftime about why 'at' cannot be used:

The description of strtotime says that it can "Parse about any English textual datetime description into a UNIX timestamp". Be careful, however,  when using "plain English". I was puzzled over why strtotime("June 23, 2003 at 12:00PM") returned a timestamp corresponding to 9:00 AM Central Time, until I realized the "at" was being interpreted as Azores Time or GMT+002. Writing strtotime("June 23, 2003 12:00PM") returned the correct timestamp.
=================================================================
Also I think Derick Rethans has recently checked in the new strtotime() implementation in PHP-5.1-dev, so may get different results between 5.1-dev and PHP4.
=================================================================
So the only unresolved questions I have for strtotime() in PHP-5.1-dev are whether these 3 formats should work:

- '%A %B %e %Y %r'
  e.g.: 'Friday July  1 2005 10:00:00 AM'
  shouldn't the weekday be assumed to be part of the format string, rather than a modifier?
  shouldn't the current timezone be assumed, rather than GMT?

- '%r %A %B %e %Y'
  e.g. '10:00:00 AM Friday July  1 2005'
  shouldn't the weekday be assumed to be part of the format string, rather than a modifier?
  shouldn't the current timezone be assumed, rather than GMT?

- '%r %B %e %Y'
  e.g. '10:00:00 AM July  1 2005'
  shouldn't the current timezone be assumed, rather than GMT?

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

No bug here, "AT" is used as timezone abbreviation.

(Nick, please do not add non-related issues to the same bugreport but open a new one if you think there is a bug).