There is a vast difference between PPL and ATPL exams. The PPL written exams can be done in a week or two if you get your head down. ATPL usually takes a minimum of six months are the content builds upon the PPL material. You cannot enter the ATPL exams unless you have a PPL from somewhere although it doesn't have to be JAR. You also need to complete an approved course of study unless you have an ICAO ATPL and a significant amount of airline experience.