preg_match() problem...

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For some reason, when it does the preg_match() it doesn't pick up the last . after p.m. ...why?

 

<?php
$str = "Meeting with Bryan and Co. June 10th from 8:00 a.m. to 9:00 p.m.";

if (preg_match("/\b(from)?\s*([0-9]{1,2}:[0-9]{2})\s*(a\.?m\.?|p\.?m\.?)?\s*(to)\s*([0-9]{1,2}:[0-9]{2})\s*(a\.?m\.?|p\.?m\.?)?\b/", $str, $matches)) {
print $matches[0];
$str = preg_replace("/\s*".$matches[0]."\s*/", " ", $str);
}
?>

 

Which outputs:

 

from 8:00 a.m. to 9:00 p.m

 

What happened to the trailing .?