Round datetime to last hour

If you are using PHP's Carbon DateTime library (which you really should - https://github.com/briannesbitt/Carbon )

You can achieve it easily using

Carbon::now()->minute(0)->second(0);

Since you already have a Unix timestamp $d, most efficient way is to use only arithmetic instead of date functions - especially if you're going to loop through a result set.

$hourTimestamp = $d - ($d % 3600);

Modulo operator gives you the remainder which you subtract from the timestamp to get hour timestamp.

In that case a simple substr could do:

echo substr($date, 0, 13) . ":00:00";

Try this,

$date = "2013-04-20 16:25:34"; 
echo date("Y-m-d H:00:00",strtotime($date));

CodePad Demo.