Try the following:
startLive = new Date(<?php echo strtotime($start_date)*1000; ?>);
Explanation:
The PHP strtotime
function returns a Unix timestamp (seconds 1-1 to 1970 at midnight).
A Javascript Date()
function can be created by indicating milliseconds from July 1 to July 19 at midnight.
So, multiply the seconds by 1000 and you get the milliseconds that you can use in Javascript.
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