for a simple implementation to Fade out the Success message i wrote my first plugin.
The Download is available
Apex 5.1 FadeOut Success Message
Import the Plugin
Create a Dynamic action on Page load
go to the true block and choce by action APEX Fade Out
after that you can set your display Time in ms.
I have got an info from Shakeep there is a function in the API Oracle Apex Api FadeOut to fade the succsess message.
I Would say this Plugin is for all they are not familia with jequery and want a simple quick implementation.