Designing a fade-out or and auto-close of a message -- a form of "anticipating" behaviour -- is a greater challenge for your design and designers.
I would
- start with just making it easy to dismiss, and not auto-close it
- try get a feel for if it is needed make it auto-close, by letting users use it over time,
- then, if needed, make it fade away
It all depends on the situation, and on how your users will end up using your system. You would decrease the risk of failure -- for example users finding it hard that things are "blinking" too fast or not grasping exactly what happened -- by choosing not to auto-close it.
Related question: Is it bad design to hide a form's success message after a short time?Is it bad design to hide a form's success message after a short time?
