The correct option is Evaluation period.

The Evaluation period is the lookback window that a static threshold alert uses to examine past metric values and decide whether the threshold condition has been satisfied for long enough to open an incident. When you configure a threshold alert you set how long the metric must remain above or below the threshold and that duration is the evaluation period.

The Cloud Monitoring alignment period refers to the interval used when raw metric points are aligned or resampled into fixed time buckets and it governs how individual data points are produced rather than how long an alert looks back.

The Timeslice concept usually denotes an individual aligned interval or a single slice of data within a larger series and it is not the total lookback duration used by the alert policy.

The Aggregation window describes how metric data is aggregated or reduced over time for visualization or processing and it does not represent the alert evaluation duration that determines when an incident is triggered.

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