You need to keep in mind the persistence of vision i.e output should stay for atleast for 10 ms or more. .

Recently I had to recode a LED sign to remove flicker. In that process I had the opportunity to poll most employees at various update rates, here are the approximate results:

50 Hz 100% saw flicket
80 Hz 50% saw flicker
100 Hz 10% saw flicker
120 HZ 0% saw flicker

based on this I recommend a minimum time of 20mS for each state of the LED.

Have fun

Erik