Change over time?
It may have a tear on it, letting trapped air out too soon.
There are five gallon flappers,
and adjustable flappers, 1.6 gallons, to 3 gallons or so.
Flapper on a toilet used to work fine. Recently it started closing too quickly, and only letting a little water out of the tank unless you held down the handle. Adjusted the chain as short as it would go and it didn't really make any difference.
Why would flapper open time just change? Any suggestions on what to do, look at or replace?
OK, so the next thing to do is to replace the flapper. We'll try it and see what happens. Thanks!
Flappers deteriorate. You didn't mention how old it was. I usually think about 3 years is the average flapper life, assuming that chemicals weren't used in the toilet tank. An old, misshapen flapper can flood a house if it blocks the emergency overflow inside the tank. I highly recommend that old flappers be replaced immediately.
I had one customer who had just replaced all the floors in his house. He even pulled up the toilets and reset them. But he didn't check the flappers. The floors were barely finished when a fill valve stuck open and the old, swollen flapper blocked the overflow. His insurance company wasn't at all happy.