Aite, I do not understand the plan here.
Time machine is broken. They are stranded in prehistoric American continent. But they need to travel from prehistoric America to Prehistoric Japan, with the hope of using the time machine there. So, their time machine can travel through time, but not space. So why risk dinosaur era when you can time travel to 20th century America and then use the Magic Door which have 20th century map loaded into it and just go to Japan that way?