Very informative link.
Start your fire early in the day if you want to bake 25 pizza's. After 2 hours, your oven will be hot but I think it is hot enough for baking 25 pizza's in a row. The site suggests that it can take up to 4 hours. You do not know the oven you are going to work with, it for sure won't hurt if you fire it up 6 hours or even more before the start of the party. That will make sure your oven will be completely saturated by the time you start baking and it will not cool down after pizza number 10. It will cool down ofcourse, but it won't take as long to be up to temp again, and you will not even notice it if you bake pizza's at a different spot every time.
Get some help with someone preparing the pizza's. People enjoy it and that makes that you can continuously work the pizza's. If you heat up the oven as suggested, they will need your full attention.
Don't aim to do 4 pizza's at a time. Sure, the oven can handle it, but I can not and my oven is also fitting 4 pizza's. (Did not want to offence you by saying you probably can't
) They bake almost instantly (should be in the 90 seconds range, maybe 2 minutes) If you have to shoot 4 pizza's in, the 1st one is finished by the time you properly placed the last one. However, usualy, because of the life fire in the oven, your pizza's also have to be turned and taken care of. As said, I can not do that with 4 pizza's at a time and honestly, if you let people make their own pizza or have 1 person making the pizza's, you will not get 4 pizza's at the same time so you don't have to do it.
Thats the way I do it. With the party's I host, there are always 1 or 2 people enjoying the making of the pizza's (plus all the kids that are there), and also 2 or 3 that like to handle the pizza's in the oven. The rest just eats the pizza's that are served and enjoy the party. We usualy also do 25 pizza's for roughly 30 people, after about 1 hour, most people have had enough. The whole baking proces usualy takes roughly 2 hours from the first to last pizza.