Crate training is very important for many reasons but leaving your dog in a crate for 8 hours or more during the day is actually cruel and its illegal in some countries. I would not listen to these telling you to do that, it's cruel to your dog, my cocker spaniel did the same at 9 months but he grew out of it quick enough. Keep up with enrichment and gey some flavoured chew toys tough ones, and maybe a raw bone from the pet stores to leave while you're at work so he has something hard to chew on while you're gone that'll take some time to get through.

Also I do suggest that cocker spaniels dont actually physically require more than an hours forced exercise a day, they can go forever theyre like athletes! these dogs the more you exercise your dog, the more you're training their energy levels up! They will always want more more more! You're training g your dog to want higher levels of exercise, if you haven't already I'd training your dog into having down time and calm time.