The recommended cooking time for a beef joint in a slow cooker is generally between 5 to 8 hours on the LOW setting, or 3 to 6 hours on the HIGH setting. For example, a large topside joint usually takes about 5-6 hours on LOW or around 3 hours on HIGH. If the joint is a brisket, it may take up to 8 hours on LOW or 6 hours on HIGH. It's important to check the internal temperature for doneness: medium-rare at 55°C (131°F), medium at 60°C (140°F), medium-well at 65°C (149°F), and well done at 70°C+ (158°F). Resting the beef for 30 minutes after cooking is also recommended.
For best results, seasoning the beef, optionally searing before cooking, and adding stock and vegetables to the slow cooker are common steps. The cooking time may vary depending on the size and cut of the beef joint as well as the specific slow cooker used.