Wait, didn't Mackie say he seen the script from his interview about a month ago
While the newbies like Mackie, Grillo, and VanCamp will probably need time to get into their character, we don't actually know how big of the roles they really are in the film. Based on the title, the main characters will be Cap and Winter Soldier. Now, I don't think Evans will need much time to prepare in term of acting since I don't see Cap's mindset change too much from last time. For Stan, while his character does go through a big transformation into what probably will be a tragic and conflict 'villain', it also seems to be Stan's cup of tea anyway.
The men seem to have been bulking up already. So unless there are scenes that require the actors to be expert at something, I wouldn't be freaking out about prep time for them just yet.