The choice of a complement can be tested by four questions:
1. Which aspect of the act does the listener need?
2. Does the speaker actually know the proposed detail?
3. Will it add true and useful information?
4. Will it clarify the purpose or distract with irrelevant particulars?
“Sāfara Zayd” may suffice to announce a journey. If the time of travel is important, “Sāfara Zayd laylan” contributes the relevant restriction. A location phrase would answer a different question.
This exemplifies fitness to the occasion: both specifying and deliberately declining to specify can be apt.