Most crock pot recipes say 6-8 hours on low. If you want to add more herbs, using fresh at the end will brighten up the sauce. When I have simmered pasta sauce all day, it has reduced and become a thicker more flavorful sauce. Another tip would be to put frozen meat in the crock pot on low and let it cook whle you go about your day. This works out well for me and the meat is usually done by 7 hours, then I shred it and turn the crock pot to "keep warm".