I am planning on taking a day trip with my son to Boston next Friday. He is 5 and getting somewhere with him on time can be unpredictable. I am hesitant to buy tickets beforehand for a certain time and miss it since they are non-refundable. The website says there are always tickets for sale at the booth but it is recommended to go when the booth opens (8:30am) because they can sell out quick. Has anyone found this to be true? If we get there in the afternoon, is there a chance there will be no tickets left?