Probably never. They'd most likely prefer you purchase those episodes from Apple.
An appropriate followup question would be: what about Netflix? They provide movies and TV show that Apple also provides. In this case, I think Netflix was included because it has deeper market penetration and therefore greater importance to prospective consumers. In short, you want Netflix streaming on your set top box or customers will not consider your product worthwhile.
But that's just my opinion and Apple could add Hulu (or more likely Hulu Plus) to their lineup tomorrow.