I have written this Javascript to convert a timestamp to something readable. It works perfectly. However I need to do it with PHP but don't know how. Obviously I don't want an alert of the time, but I'd like to have it as a PHP variable. Any ideas?
<script>
var bmsTime ="39845.03";
var date = new Date('31 dec 1899');
date.setTime(date.getTime() + bmsTime* 24 * 60 * 60 *1000);
alert (date);
</script>
Use the date function, it takes an additional parameter called timestamp. But in php timestamp is number of seconds, not milliseconds as in javascript, so divide it by 1 000:
echo date('l jS \of F Y h:i:s A', $javascript_timestamp / 1000);
The short answer: You cannot properly do this, as you do not know the timezone the browser/client is using.
Long answer (using the server timezone - or whatever is configured for PHP):
$bmsTime = 39845.03;
$date = mktime(0, 0, 0, 12, 31, 1899);
$date += $bmsTime * 24 * 60 * 60; // $date are the seconds relative to "the epoc" (1970-01-01 UTC)
echo date('c', $date);
var_dump(mktime(0, 0, 0, 12, 31, 1899)); returns int(-2209075200) here, so it works for me in PHP 5.3.5. Maybe: Before PHP 5.1.0, negative timestamps were not supported under any known version of Windows and some other systems as well. Therefore the range of valid years was limited to 1970 through 2038. -- php.net/manual/en/function.mktime.php