<PackageReference Include="System.Reactive" Version="7.0.0-preview.1" />

System.Reactive.Concurrency.IScheduledItem<TAbsolute>

public interface IScheduledItem<TAbsolute>
namespace System.Reactive.Concurrency { public interface IScheduledItem<[Nullable(2)] TAbsolute> { TAbsolute DueTime { get; } void Invoke(); } }