Hello my name is Jenny and I am happy to help you today. It is imperative that you raise your claim on time, i.e. the day before 3 months after termination has expired.
You do not need to wait for your employer to respond to your appeal, if you do so and miss the deadline the employment tribunal will not hear your claim.
If you have any further questions about this please do ask. If I have answered your question I would be grateful if you would take the time to rate my answer. Thank you and all the best.