Which notation best represents asynchronous message triggers without immediate execution occurrence in UML Sequence Diagrams?

In UML Sequence Diagrams, activation bars (execution occurrences) are used to denote the period during which a lifeline is performing an operation. When modeling asynchronous messaging, an open-headed arrow indicates that the sender does not block for a response.

A design challenge arises when a message is sent asynchronously to a receiver, but the receiver does not immediately begin processing the request—for example, when the message is placed in a queue or a buffer before a separate worker process triggers the actual execution.

Does the UML specification provide a standardized way to decouple the arrival of an asynchronous message from the start of the execution occurrence? What is the recommended approach to visually represent this latency or queuing state without implying an immediate active state on the receiving lifeline?