If the withdrawal is made during the bidding period, the SCSB deletes the bid and unblocks the application money in the bank account. If the withdrawal is made after the bid closure date, the SCSB will unblock the application money only after getting appropriate instruction from the Registrar, which is after the finalization of basis of allotment in the issue. In the former case, the unblocking of your ASBA funds is immediate but in the latter case, it may entail a few days for your money to get unblocked. In case you wish to withdraw it is always better to withdraw during the bidding process itself.