When can you send a single-send journey using Journey Builder?

In Journey Builder, a single-send journey allows you to initiate an email or message to a specific audience on-demand. Sending immediately means that once you configure your journey and select your audience, the communication can be dispatched right away without any delays or needing to schedule it for a future date or time. This immediacy is particularly valuable for time-sensitive communications, promotions, or when responding to current events.

The other options reflect different concepts or scenarios that do not apply to the immediate nature of a single-send journey. For instance, scheduling for a future date or time involves creating a different type of journey or setup that allows for advanced planning rather than instant execution. Similarly, sending at random intervals or based on whimsical criteria like lunar phases does not align with the practical application and scheduling capabilities of Journey Builder.