If time travel is a feature on the worlds you write about, how far back can your characters go? Can your characters deliberately choose to extend the era in which they're officially allowed to go? What rules must they stick to before transporting themselves anywhere? And what happened when it goes wrong (it's bound to at some point, yes?).
What counts as our medevial times for your newly created world/town? How far developed is your fictional world? Are the press in your world leading lights or a pain in the neck or both?