Yes, the system transitions from State A to State B every time and I am thinking that the time duration between the states may be something which could be modeled as a normal distribution.

Another way, will be to model two poisson processes, one each for state A and state B, and get the rates of those distributions. And system probability distribution of being is either state A or state B is generated as joint distribution. I think this may be a better approach and the time duration between states may not be close to normal.

Yes, the system transitions backs from B to A.

Another example of the system events counts

Thanks