Hello Meenal,
National Testing Authority (NTA), the exam conducting body of JEE Main will be allotting the date, shift and timings for JEE Main 2019 January exam randomly to all the registered students.
Candidates will not be able to do the slot booking for the exam.
The admit card for JEE Main 2019 January session will be made available online from December 17, 2018, onwards. You can check all the information regarding the examination venue, slot, date, timings, etc. from the admit card.
Good Luck!

NTA shall give preference of nearest centres and then students can choose tgeir best preferred centre as per allocation. Time slots for JEe Main exam is fixed as shared bekow for Both Papers.

https://engineering.careers360.com/articles/jee-main-exam-centres