Hello! We are planning a day trip from Paris to Chartres in late November (likely the 28th or Dec 1) - can someone kindly remind me how the TER tickets work? Is the motivation to book ahead of time solely to prevent certain times from selling out? Or is the price also subject to increase? And, regarding return time, are you locked in to the time you select at booking or are they flexible if you were to take an earlier or later train?
Thank you!! Looking forward to seeing the illumarny displays!