Of course, the extra designers will be a valuable help during this high-intensity day.
However, please keep in mind that despite the similarity of tools (e.g., software like Figma), it’s not exactly the same job to design the interface of a long-term app and to rapidly prototype a new business idea in just one day. This requires a high level of seniority. That’s why a designer from Design Sprint Ltd is always present on day 4 of our design sprints.