SLA = Service Level Agreement - The response time configured within the Conversational Cloud to handle messaging conversations for either all conversations (default), urgent conversations, or first time consumers. The SLA can be set per the account level (default) or be overridden per skill.
TTR = Time To Response -- This time is set according to the current shift status (online/off hours). If the shift is currently active, the TTR equals 0. If the shift is currently inactive, the TTR equals the time until the next shift will start.
ETTR = Expected Time To Response - The expected response time when the consumer will be answered by an agent. The ETTR is displayed to consumers during a messaging conversation via the Automatic Messages mechanism. ETTR = TTR + SLA.
For example:
If the default SLA is 1 hour and the account is currently on an active shift, the ETTR = SLA = 1 hour.
If the default SLA is 1 hour and the account is currently offline, and the next shift will begin in 12 hours from now, the ETTR = 12 + 1 = 13 hours.