It's extremely recommended to put brackets for if, else, loops, and functions under the statement. Also, when verifying if a variable exists, use isset(). If you just want to see if a variable has a value, check with the ! (bang) operator in a boolean statement. For strings, use empty().
Here is your code. I'm not sure what you're trying to achieve with the empty IFs, but you were missing the last bracket.
if ((time() - $check[timestamp]) <= 15)
{
eval("standarderror(\"".fetch_template("confession_error_flood")."\");");
}
$DB_site->query("
INSERT INTO confessions SET
text = '".addslashes($message)."',
userid = '$conf_userid',
timestamp = '".time()."'
");
}
} // was missing