There are two different types of animation blending in Track View: Cross-Fade blending and Gap-Blending.
This blending method automatically kicks in if two animations overlap each other. The blending affects the whole section where the animations intersect – the "weight" of the second animation will steadily increase towards the intersection's end. At the start of the 2nd animation the weight for the first/second animation is 100/0 and shifts linearly until the end of the first animation to 0/100. See the illustration below:
This blending method can be used to blend from the end frame of one animation to the beginning frame of the next animation.
Half a second proves to be a good value for most blending operations, but you can choose whatever size (= blending time) you want.