Quote -  This can be done using a Blender Node with 2 different 2D Image Map textures plugged into it. You also have to click on the little key's in the material room that turns material animation on and off. Then it's simply a matter of changing the strength of one image map to 1 while lowering the strength of the 2nd image map to 0 over the course of the animation.

I agree the blender node is the way to go, but you can save a step by simply animating the blend level of the blender node itself.  When the blend is at 0, Input 1 should be the only source you see, then when it is at 1, Input 2 will become the texture.  This way you only need to animate 1 value.  This will help later on when you start chaining multiple blender nodes to animate multiple textures in sequence

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