Is it okay to prepare "Cannelloni with Spinach" recipe and put it in fridge BEFORE baking?
Most casserolles are OK to be stored in the fridge before baking, or even made several days ahead and frozen. Assemble it, cover it well (e.g. with plastic wrap) and put it in the fridge. When you are ready to eat, you can bake it as usual, but you will have to make the baking time longer, because it starts out at fridge temperature, not room temperature. I can't tell you how much longer, in the worst case you will have to try cutting into the cannelloni a few times to see if they are done.