Here you can see that it works in the preview;
http://puu.sh/hUDcN/279433ab08.jpg
http://puu.sh/hUDeY/e9c140330d.jpg
Here is how I am doing the alpha lerping, Timer1 Delay is the timer delay so it maps the range of the timer from 0 to that delay. I also tried to change the variable directly in the AnimBP and it did change the variable but nothing happened to the mesh.
http://puu.sh/hUDis/6d136920a8.png
Here is the modify bone setup: