Yup, that happened to me a few times. Just got to keep on doing it. Once you click on a specific time after clicking on the date, it will hold that table for you for 9 minutes. That will give you plenty of time to choose beverages and make a payment.

Be warned that if you click on a time and it gives you the 9 minutes, and then you decide that time doesn't work for you, you must log out, clear all cookies and cache, and then log back in. I didn't do that, and when I thought I was buying tickets for later in April it turned out it kept the previous table I had thought I'd canceled. That's why we went last weekend instead of a few weeks from now.