The expected response date is for chargeback. So it the date by which issuer can expect a representment. So it is the same as SLA on Awaiting Acquirer response.
As per MCOM, the timeframes is 45 days and to adjust for delay in record coming in the queue we have a DSS which can be set by each issuer. For example if the acquirer represents on 45th day, MCOM processing the record and placing it in queue and issuer reading the queue could take 2-3 days. So a DSS has been given to issuers to adjust for the delay on top of the 45 days.
So this date is 45+DSS days from chargeback submission date