To get the one decial place in php can be achieved by using the round function.
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How to get timestamp before one week from now in PHP
You can get the timestamp value for before seven days from a certain date by substracting the timestamp.
Lets suppose you want to find out the timestamp for seven days before 27th or some other date. We have to substract the timestamp that counts seven days from the timestamp of the date from where we want to find out the result.
<?php
$before_seven_day = $date_timestamp - (7 * 24 * 60 * 60);
// $date_timestamp is the date from where you found to find out the timestamp.
?>