hi bro 

yes as the both exams are held by the cental government there will be no same dates for any two exams conducted by the central goverment , the jee mains exams will be held on april 21 and upsee2019 will be held on june2nd so you will have a very good time for the preparation also and upsee exam is also a very good choice , but follow the good books and prepare for it and mainly write the mock tests and try to solve the previous year question papers so that you will get an idea that the model of questions will be given in your question paper and you acn easily solve it and do you know actually 100 percentage of questions come only17 percentage of syllabus and sostudy smart but not hard , hope you will have a successful future and all the best for your exams BRO