If you ever wondered why the slow cooker needs more time than in the instructions, maybe you should be careful how you handle the lid. If you take off the lid from the slow cooker, part of the heat will be left out and this messes up with your cooking times. Of course, it is tempting to open the lid and check on our dish, but it turns out it does more bad than good if we do that.
So, if you manage to resist the temptation to stir the ingredients around or just to check it, it should cook just fine with the intended instructions. If you truly want to check on it, you should do so when there is less than an hour until it is done.
Generally speaking, if you do not overfill your pot (anything over a half and three quarters is considered overfilling) you should have no problems with your slow cooker and you will just have to withstand the delicious smell that fills your whole kitchen just a little bit more. Patience is the key!