On most trains, the maximum hold time is 7 days and that assumes that you're more than 7 days away from the date of travel. For Acela and trains on the NEC, the hold time may be less. As for traveling around the holiday's, especially the Thanksgiving weekend, if you haven't booked by now you may not be able to get a seat. But whatever you do, don't wait until we're really close to the holiday, you're almost certain to get shut out.