a juz is just under 30 pages long (depending on the quran design, i.e. how big the pages are), im referring to the pages that are half a regular sheet of paper, im talking 8.5 in. by 11 in. The time obviously depends on the person, on average it takes me 40 minutes to read one juz
The most common design is where each juz is about 20-22 pages. It also takes me about 40min to finish 1 juz.