Thinking about taking some AP still time to register?

<p>Post title speaks for itself, I just recently discovered AP was wondering if it improved chances at US unis at all and if if I still have time to apply to take exams this summer? If not is it possible to take exams this fall? and is it doable for me to revise the topics for the subj I may decide to do over the summer hols? Thank you for ur help</p>