Well if you are sure $jj_post is always going to be an array, and that it will always contain an stdClass object, then you should access like so:
$jj_ID = $jj_post[0]->ID;
But it is not always so sometimes. You may not always know the contents of a variable so you need to do some checking to verify that you access areas that are safe and available.
How long the code is shouldn't be an issue if it performs the job well.
In my opinion, you have two alternatives:
$jj_ID = @$jj_post[0]->ID;
This ensures that the runtime errors are silently handled, and not thrown to the standard output.
Another way would be to check absolutely for presence of each type:
$jj_ID = "";
if(is_array($jj_post))
{
$jj_post_id = $jj_post[0];
if(!empty($jj_post_id))
{
$jj_ID = $jj_post_id->ID;
}
}