expireTime property

The snapshot is guaranteed to exist up until this time.

A newly-created snapshot expires no later than 7 days from the time of its creation. Its exact lifetime is determined at creation by the existing backlog in the source subscription. Specifically, the lifetime of the snapshot is 7 days - (age of oldest unacked message in the subscription). For example, consider a subscription whose oldest unacked message is 3 days old. If a snapshot is created from this subscription, the snapshot -- which will always capture this 3-day-old backlog as long as the snapshot exists -- will expire in 4 days. The service will refuse to create a snapshot that would expire in less than 1 hour after creation.

Optional.