As seen in the episode 4, Yaz and Dan were transported into 1901, along with the professor. What I want to know is in that three year time gap, why didn't they go to America? They were so worried about finding the doctor, but in 1903 (which happens between when they arrived in time and when they are shown in survivors), Yaz had been with the doctor at Niagara Falls, helping Tesla with the Skithra. It would certainly mess up some timelines but the timelines are already ridiculously messed up sooo... Even if they don't pull the doctor away permanently, they might be able to borrow her tardis to travel to immediately after revolution of the daleks and pull out the doctor to stop whatever was going to happen. Now, it's highly unlikely that this would work, but I'm surprised yaz didn't even think of it. At the very least, they could have explained the situation and asked for advice.