Time is allowed to pay for parking, or else nobody could ever park legally. You now have a choice, (1) pay the discount, or (2) wait for the Notice to Owner and submit reps against that. These reps will be broadly the same as your initial challenge, but updated to answer what they said in their rejection letter. Redbridge normally re-offer the discount at this stage, even though they don't have to. However, with councils so greedy for money nowadays, the only place you'll get an unbiased judgement is at London Tribunals with the full PCN penalty in play. If you win you pay nothing, if you lose you pay the full PCN penalty but there are no additional costs.
Is the car yours, and is the V56C Registration Certificate up-to-date addresswise ?