The SLA in Freshdesk will not be per response/ reply but per ticket. A ticket is considered as one issue and the SLA for that would be decided by the priority that you set for the ticket. Based on the priority the SLA will change. Also, from the Estate plan you can setup multiple SLA policies and based on the conditions set, the tickets will be impacted as well. If there are different issues discussed in the same ticket, you can split the response into a new ticket.