Slow Refresh Rate

Hi, I am using a 96x64 white light OLED, with adafruit_SSD 1331 library and Adafruit_GFX.h for my project.

However, I am having problem with the clear screen function. The idea behind is basically using fillRect function with black pixels.

Is there any ways I can speed up the filling pixels? I really need this to work because I am refreshing my display to show the time remaining.

Below is my code.

What may be the factor affecting the refresh rate?

OLED_Control_revised.ino.ino (18.5 KB)