It depends on which way you cook them! On the stove top it can take 1, 1/2 hours - to 2 hours. In the slow cooker, being cooked on high it can take 4 hours. Other factors that can affect how long it takes for collard greens to get tender is how much broth is used and the type of greens. Some collard greens are less tender than others. So this will affect the cook time.