What's the rush?
They seem to be in quite a hurry to get back to 1357, like stuff in the past is somehow happening in parallel with current time. Why couldn't they take a couple years to assemble a team, train them, etc and go back at their leisure? It was the same 1357 they were going back to.
Or was this explained?
If only I had more time... Wait, a minute, I got all the time I want! I got a time machine! -Marty McFly