It's a complicated one, but his confidence in her should serve as some serious encouragement. Naruto learned Rasengan in a week, he believes with Sakura's stronger chakra control and intelligence, not to mention her strong desire to improve, she can master Water Dragon Bullet in that short amount of time. I don't expect her to even come CLOSE to doing it today, especially with the conditions Kakashi is going to put her under. It's going to frustrate her, and it'll be expected, but she'll come to discover that Tsunade asked Kakashi not to take it easy on her. If she can survive Kakashi's expectations, she'll be ready for the conditions Tsunade will put her under. Yes, have Sakura do that, Tsunade will have asked Kakashi to prepare Sakura to become stronger. As it stands she's pretty unremarkable, but if Kakashi works with her she'll be very capable. It might seem mean to think of Sakura in that way, but it's true that compared to her teammates she has, at this point in time, nothing really going for her. Kakashi and Tsunade are going to work her to the bone! So yes, go with that.

I'll be waiting on skype~