Unfortunately I haven’t tested this particular screen so I’m not sure how long it takes the screen to be filled with a single color. My guess is that 20s is a bit high, did you do any changes to the code, what code are you using? Can you test this TFT LCD in another board such as an Arduino UNO or similar?
I have tested the code with TI controller TM4C123G which is running at 80MHz. The time taken to fill up the screen is less than 5s. However when I port over the code to Edison, I did make changes in the driver code in order for it to work.
I am just wondering why Edison which is running at 500MHz is filling up the screen slower than a processor running 80MHz.
Btw, do you come across any TFT LCD driven by Edison? What is the time taken to fill up the screen? It is possible to complete in miliseconds?