On average how long will a sundown syndrome event last?

I am sorry to tell you, it will only get worse.   At first a few hours, but over the last 3 years, it has gotten to the point it can go all night.   If you have not done so already,  have your LO spend time outside as much as possible and use lightbulbs with daytime light in LO room.    cut off TV or computer with blue screen or use special eyeglasses to keep out

Katie's experience, I think, is pretty extreme. For something like that meds may have helped. But like the name, it can continue all night.

This sounds hellish.

With my Dad..it lasted until he was so tired he fell asleep.

usually started about 6 pm. After putting him to bed, he would be back up within an hour....yelling, banging stuff, even threw coffee (cold) on me. This could go on till midnight or 1 AM. I finally hid the TV remote and tripped the circuit breakers for the kitchen. He would turn on everything at high volume and then turn on all the appliances too. So, instead of LOUD TV and electronic noise I would get him yelling and throwing things.

for my Dad it was 6-7 hours before he would be too tired to continue.