Bad news

At that speed it should be apparent to the eye. You might need to be around 10 times faster. Experimentation may allow you to operate more slowly.

You are currently operating at about 3.3 frames per second (300ms to complete the cycle).

Movies use 30 frames per minute to blend motion. We uses that as a base when mutliplexing displays. (I'm no fan of multiplexing LEDs for reasons I won't go into since I can't share my solutions there for commercial reasons.)

Of course you also have to consider that you'll have reduced illumination due to the dutycycle of the display. Current consumption will be reduced, noise on the power line will be increased. Noise on the power line may affect the accuracy of your ADC.

-Jay C. Box