What is to estimated time in the oven?

I have not used this specific recipe, but I make my own tomato paste in this same manner. 10 pounds of tomatoes will take a good 3-4 hours to reduce down to a paste. It all depends on the amount of liquid they contain to start with. One way to help remove some of that excess to start with is to freeze the whole tomatoes overnight and then let them thaw in a clean dish pan, large stockpot, or some such container. As they thaw you can slip the skins off a lot easier, and they will give off a ton of the liquid. You can save the liquid for soup making, by the way. Once your tomatoes are skinned, it's fairly easy to separate the seeds and pulp in the food mill. Once that's done, just proceed with the recipe as written.