H1B CAP Exempt Processing

I was in USA from Apr 2015 to July 2016.In that period my petition was extended and was valid till Aug 2017. I could not travel after i came back in Jun 2016.The petiotion got expired. Now i want to go for CAP exempt.

How much time it time it takes to process in Normal and premium category?

How is the probability for going in premium category? Which one is better for an Computer science back ground (Normal or Premium). Please advice.