For Riverbelle Terrace, usually all of the front row tables are taken by 5pm. My daughter & I went last Saturday & got there @ 4:45, and someone was waiting for the people to finish eating at the last table, so got it before we could. We ended up at a second row table, and had an umbrella stand in our way (they don't take them down).
Some friends of hers joined us to watch the show, and we had an extra chair, which I offered to a little six year old. Her parents stood at the back of the patio while she was able to enjoy the show with us -- her first time to
Disneyland.
They only allow a limited number of people on the patio, and CMs will monitor the ins and outs after a certain time (maybe 7pm?)
Still, we enjoyed the show.