According to the official information available it would take around 4-5 working days and in few cases it is around 15-20 days also. So I would suggest you to once contact with the contact number or email id present during the working days.

This are the options for withdrawing.

There is no option of withdraw of an accepted/allotted seat after the announcement of last round of seat allocation (for IITs only).

For exercising withdraw option, candidates have to complete the following two steps. (A) On the JoSAA portal fill-in the Bank Account details to which the seat acceptance fee shall be refunded and upload an image of cancelled cheque/passbook of the same account in JPG format. (B) Candidate needs to confirm on the JoSAA portal that they withdraw from the seat allocation process. Once the candidate has withdrawn, the seat allocated to the candidate shall stand cancelled. The candidate will be out of the JoSAA process, and she/he will NOT be considered in any further rounds of allocation.