The correct option is RTO.

RTO stands for Recovery Time Objective and it specifies the maximum acceptable length of time that a critical system may remain unavailable before essential operations must be restored. Organizations use the RTO to set recovery targets and to design recovery strategies such as failover, alternate sites, or prioritized restoration sequencing.

RPO is incorrect because the Recovery Point Objective defines the acceptable amount of data loss measured in time and not the allowable downtime. It answers how much data the business can afford to lose rather than how long systems can be down.

SLA is incorrect because a Service Level Agreement is a contract that defines expected service levels and obligations between a provider and a customer. An SLA may reference objectives like uptime but it is not the internal business continuity metric that sets the allowable downtime limit.

MTTR is incorrect because Mean Time To Repair measures the average time to repair a failed component or system and is an operational reliability metric. It does not express the business tolerance for downtime in the same way that the RTO does.

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