You dont get back to your room for Horror Nights till 1am (2am some nights), which is going to make getting up early to do both in one day exhausting. Volcano Bay you really want to rope drop so you can get the rides knocked out and then relax in river or wave pool. I would actually recommend doing Volcano Bay chill and save your energy, then Horror Nights same day. You CAN get Islands and Studios done in one day (assuming done means rides and not shows) with Express if you get lucky. It just depends on how Hagrids and Velicoaster plays out.