(dynamicMember key: KeyPath) -> Duration where P : ProgressManager.Property, P.Summary == Duration, P.Value == Duration { get set } ``` ## Parameters `key` A key path to the custom duration property type. ## Overview This subscript provides read-write access to custom progress properties where the value type is `Duration` and the summary type is `Duration`. If the property has not been set, the getter returns the property’s default value. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)