I need to bake 10 slabs of barbecue ribs that will be finished off on the grill.
The recipe calls for baking each at 250 degrees for 2 hours. Can I bake 2 or more ribs at one time? If so, what adjustment should I make to temperature and time?
If the oven is large enough, you can bake as many slabs as will comfortably fit on one tray or oven rack without any adjustments.
If you need to seriously cut the total baking time, you could use even two trays at the same time, but in this case, you need to make sure the ribs get enough heat from all sides, which means swapping trays and turning the ribs occasionally and probably baking for a bit longer - I'd guess fifteen to thirty minutes - to compensate for the less-than-ideal heat exposure. I'd leave the temperature setting unchanged unless you notice excess or too little browning halfway to the parbaking.
Not part of your question, but probably worth mentioning, as I assume you will be serving the ribs to many people:
Whatever method you finally choose, note that such a large amount of ribs that will be ready for further processing will need some extra actions to ensure all the meat stays safe and not in the danger zone for more than two hours. So you might want to think about either keeping your meat hot (above 140F/60C) or cooling it down quickly (below 40F / 4C). Find more details and useful links in our canonical post.
And if you're going low & slow in the oven -- there should be no change in time or temperature. So long as the oven can maintain the temperature, they will cook in exactly the same time, so long as you don't stack the racks directly on top of each other. (and it helps to stagger the sheet pans as much as possible, but still leave an inch or two of clearance at each wall)
If you're not doing the pouch method, you might be able to roll them up into a circle and skewer through them, as J.Bergen mentioned -- this allows there to be heat coming from both sides of the meat ... but I've never tried it in the oven, so I don't know how effective it is without the convection from the grill. You can sometimes get as much as 2-3x as many racks of ribs on the grill this way.
You might also want to consider a vertical rib rack, which allows you to fit more racks into the oven if you're going to be doing this on a regular basis. If you have two 5-slot ones, and your oven is tall enough, you might be able to cook all 10 at once without much problems.
Also to note -- I once did pouch cooking in my oven, but plans fell through, so I drained the pouches (which was slightly acidic), put the pouches in the fridge, then reduced the liquid into a barbeque sauce. The next day, I heated the ribs through on the grill.
If you have a small grill, and need to heat things faster, you can often fix two racks on a sheet pan, and put it under the broiler (top heat)