After acknowledging the incident, if it is not resolved in given amount of time then it will return to triggered state. Escalations and alerts will resume again.
Many-a-times, you or your team-mate would acknowledge an incident but never get around to resolving it for multitude of reasons. This is where the acknowledge timeout feature comes in handy.
You can set acknowledge timeout in minutes to all of your new and existing integrations by editing a service or adding a new service.