Well, we know the Teiflings started in Elturel, and are travelling downriver towards Baldurs Gate. We also know that Moonrise Towers is "next stop" downriver on our journey towards Baldurs Gate.
So, I guess that puts us much further upriver than where you calculate? At least according to this map.
That certainly complicate things ...
I also think it was supposed to be about 10 days away. I don't remember anybody mentioning 3.
And that would explain those things.
Its possible, i dint play for some time and in few last plays i skipped most of the conversations. :-/
I promiss i shal check next time i get there.
But, its totally possible that i was wrong. :-/