No content flashes more than three times per second
To make your website as safe as possible for all users, you must limit the amount of flashing media. Flashing content can harm the health of some users.
What this means
Don’t add anything to your website that flashes more than three times per second.
Remember, flashing is different to blinking (see Guideline 2.2.2).
There is a ridiculously complicated exception based on the user’s visual field. You should just avoid all flashing content, but here it is:
the combined area of flashes occurring concurrently occupies no more than a total of .006 steradians within any 10 degree visual field on the screen (25% of any 10 degree visual field on the screen) at typical viewing distance.Understanding WCAG 2.0
If you can work out what that means, I dare you to use it.