I forgot the fennel seeds and didn't have a very large fennel bulb (replaced it with some onion instead), and we definitely missed the fennel flavor. Overall, this turned out wonderfully! 8 hours on low in my 6 quart slow cooker was just right, and it stayed just fine on warm for 5 hours after that. Next time, I will definitely use the fennel seeds. The only other change would be maybe to leave out the olives. The barley did get very creamy, and absorbed all of the liquid in the recipe by the end of the 8 hours. I imagine it would do fine on high for 4 instead as well.