David,
Since The PM PrepCast is built in a "modular" way, it should be relatively easy for you to look at the curriculum of your class and decide which videos to watch. So what you can do is to watch all the Cost related videos in the week leading up to when cost will be discussed in your class. In that way, you will arrive fully prepared to the class and you can use the time in the classroom for a review of the material and to ask questions.
I also think that it's too early to tell, if you need to postpone your exam to after 6/22. Continue your studies, answer as many sample questions as you can and decide around 6/10 if you yourself think that you need more time or not.