public function isValidTimeStamp($timestamp)
    {
        return ((string)(int)$timestamp === $timestamp) && ($timestamp <= PHP_INT_MAX) && ($timestamp >= ~PHP_INT_MAX);
    }
public function isValidTimeStamp($timestamp)
    {
        return ((string)(int)$timestamp === $timestamp) && ($timestamp <= PHP_INT_MAX) && ($timestamp >= ~PHP_INT_MAX);
    }
public function isValidTimeStamp ( $ timestamp ) { return ( ( string ) ( int ) $ timestamp === $ timestamp ) && ( $ timestamp <= PHP_INT_MAX ) && ( $ timestamp >= ~ PHP_INT_MAX ) ; }
Checks if input string is a valid timestamp or not
@param string timestamp contains input timestamp-like string
@return bool
Checks if input string is a valid timestamp or not