The cooking time for a 2.5 lb roast in a crock pot can vary depending on the desired level of doneness and the specific recipe you're using. However, as a general guideline, you can expect it to take approximately 6 to 8 hours on low heat setting or 3 to 4 hours on high heat setting.
Crock pots cook at a lower temperature compared to other cooking methods, but they provide consistent heat and allow for slow, tender cooking. It's important to note that the actual cooking time may vary depending on factors such as the size and thickness of the roast, the type of meat, and the specific model and settings of your crock pot. To ensure accuracy, it's always recommended to use a meat thermometer to check the internal temperature of the roast for doneness. The USDA recommends cooking beef roasts to an internal temperature of at least 145°F (63°C) for medium-rare or 160°F (71°C) for medium.
For more precise cooking times, I would suggest referring to a specific recipe or consulting the manual of your crock pot for recommended cooking times based on the weight of the roast.