BDD is not given when then.
It is a way of collaboration in which technical people with non-technical, business, product people write collaboratively specifications that everyone can understand. Gherkin is a format to do that. BDD is not a new format to write specifications, but rather having conversations between developers, testers and business people. Bringing examples to the front is the way we discuss what we want our software to do. BDD is a ubiquitous language.
With ubiquitous language, you can avoid terms that are understood by some of the team members only.
Ubiquitous language is used in DDD too.
DDD is a way to model software against business processes. During an event storming workshop, which is a group modeling technique that brings together, we would tend to think about using BDD on individual user stories to make sure that we nailed down the details. And where those stories are come from.