I have an e-certificate which I would like to use for a free hotel in Los Angeles. The problem is Ill be taking a cross-country train trip to LA. This trip has a 50% chance of being delayed 1 or even 2 days . Is there a fee to change a reservation by 1-2 days? Does it make a difference that I will be using my free e-certificate for the room?

Alternately is it better to book the room the day before I am scheduled to arrive in LA? I will have wireless internet access so can do it from the train.