I make these for church breakfasts all the time. I would advise 375. let sit about ten minutes before cutting. foil them in the fridge.

And don't leave out.....that only increases the time the casserole is at an unsafe temperature. Agree with allow to sit and firm up before serving.

Leaving out a short time is not going to make them unsafe because they are going to be baked to a temp that will ensure safety. I sometimes let glass dishes that have been in the refer sit out for a short while to lessen the shock risk of a cold glass casserole being set on hot oven racks. Or I set them on a cold cookie sheet before placing in the oven.

Agree with gardengal. I make them fairly often, too. They'll be fine if left out for a short period. Let them sit out at least as long as it takes the oven to preheat...or even a bit longer. Sometimes if it's too cold the outer parts will cook faster than the cold center. Experience has shown me baking two at a time can sometimes mean just a bit longer in the oven. Just start checking at the regular time for "bubbly" and "golden." You might need another 5-10 minutes. It can often just depend on your oven, too. If you like, you can check the centers of each with a thermometer, but you should be able to tell just by looking. Also, rotating once should be enough. You don't want to open the oven too often.

This made me think of not long ago when I cooked two small rib roasts side by side in the oven. They were the exact same size/weight. It took one of them 45 minutes longer to cook. In that case I assumed it was just the density of the meat. Anyway, you'll be fine with the two brunch casseroles, but it's always a good idea to check each one.

The rule generally is food can be left out for up to two hours.

Not necessary for you to do that though. 15 minutes on the counter and then into a 375 oven should be perfect. 15 minutes to set up at the end of cooking as already said above is also perfect.

For myself I leave a lid on for a little over half of the time when cooking from the fridge. It means that I don't get as uneven results. Then I take the lid off and allow things to brown. I sometimes help it by putting on the broiler for a few minutes especially if cheese needs to brown or top needs to brown a bit. Make sure you focus completely on it if you do this last step. Watch carefully!

I don't know what everyone else uses but nowadays I almost exclusively use convection roast as my setting on the oven for browning.

https://soyummy.com/guide-long-food-can-left-room-temp/