Sorry, I think my English is not good enough to describe complex situation like this,
sorry for misguiding 
Only the part which led runs in order need slower fading time (1~13, 13~1 that part),
others are the same speed.
in this project I put led stripes inside box, and put laser-cut acrylic above it,
so when the led fade in, the pattern on acrylic will slowly shows up.
Really appreciate for answering me 