It would be 10 days after the initial campaign was run. The engagement program won't look to see whether or not the actions were completed, but merely when it began. So if you have...
Campaign - Email 1 & Email 2
Email 3
as your stream. And you have a 10 day cadence, if the cast goes out on Tuesday, then the Campaign 1 begins on Tuesday first sending out Email 1. Then on Friday it sends out Email 2. Then the following Friday, 10 days after Campaign 1 began, it would send out email 3.
That being said I don't think you can have a 10 day cadence. You can have 7 or 14 days, but I doubt 10. If you can do that let me know how.