there are about 2000 questions in usmleworld ...doing about 50 questions a day would take 40 days....i would also reserve some time to take a quick review of questions that you got wrong and try them over.

the questions really give you a good idea of long stem questions you'll see on the exam.

just keep in mind that the actual exam has both short and long stem questions. if you finish the questions on usmleworld you'll be fine for the exam.