I liked booking online, because the system will give you suggestions if your time and place is not available. It will also allow you to adjust your time if needed - it will give you two additional other available times. I like it, because it would take a human longer to do so.
The important part is to do your most important ressie first and then in order of importance. Don't be locked into your choice of time or place; decide which is more imporatant, the time or the experience. I had to take one early dining time, but I didn't care because it was all about the experience for me.
In another case, they didn't have anything available at my first choice, but it gave me one I would have never even thought of doing - and I am really, really psyched about that!