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365*60*60*24 should be a constant.
You should really improve your variable naming.

$date2 = date("Y-m-d H:i:s");

date2? Does that say anything? currentTime is more like it. Always describe what variables contain, not what they are.
Isn't $diff already the number of seconds?
Most part of the date/time checking could be rewritten to:

$seconds = time() - strtotime($key);