I know that I'm horribly anal when it comes to these things, but even when I was writing fanfic I used to CHECK details like this e.g. how long would it take to drive to Paris from Wiltshire in a sports car, and stuff like that. Most readers won't care (as is evidenced by Potter success but some will, and most importantly I WILL. It's very clear that JKR has no respect for her readers because she just writes this crap down and doesn't bother that her facts don't click together.

And yes, if they can wander around Muggle London and biff around Hogsmeade, then they could EASILY have visited the Weasleys at any time. Again, that's the trouble with magic with no rules and limitations.

That would have been a VERY good cover idea.