That’s correct. It’s also worth noting that email programs cannot be nested into child programs within Engagement Programs. But for most basic use cases, Veronica’s solution is ideal.
In this scenario you would use a Champion/Challenger email with a trigger campaign or engagement program. Add an Email Champion/Challenger - Marketo Docs - Product Documentation
I agree with Steven. Linda in your scenario I'd use a Default program with Champion Challenger. Then because Champion Challenger only works on trigger-bassed tests, maybe use an add to list or request campaign trigger to get them added to the smart campaign, and into the test. You could use this to add as many people as you like into the email send over time.
Great thanks everyone! Will test this and let you know how it goes