When a consumer sends a request to business, the obligation is complete the request and return response to the consumer within 45 days. Means end to end flow needs to be completed within 45 days. Can be extended under certain circumstances. Details here
Hence, applications are required to execute this keeping enough buffer for business (receiving request and returning response). In ACS, internal SLA which is much lower to complete the request, giving enough time to the business to return the response to end consumer. Depending on the number of requests, it takes couple of days* to return the response once request enters the queue.
