You might want to do a "test run" first before trying it out for real, just to make sure that it will work for you. A few days before I made any real ADRs, I tried it out by making a lunch and dinner reservation at the same time using two browsers at once and it worked just fine. (This is also how I learned that it will NOT work if you are trying to make two reservations using two different tabs in the same browser!) Once I was successful, I just canceled the reservations.