“If we could open up 780 days on the schedule - what new features would you like?” At this point you want the client dreaming of all the extras they never thought they’d get to have.
Then at the end you mention the 20 day delay. At this point they will feel the “loss” of the new features they just imagined. It’s an extremely powerful sales technique that works almost everywhere.
Given your earlier comments about the extra 20 days they seem particularly susceptible to this technique.