I have never let the whey sit for any length of time, so I can't help you there, although if it is going to be kept in the fridge you might get away with it.
I usually make it while I have everything going making cheese.
In the recipe exchange section on page three, Cheese Head has a recipe for ricotta. It says to keep it at a temp for 1 hour. Personally I have never done that, so I don't think that is imperitive. I add 1 cup of wholemilk to what ever whey is left over, usually from a 10lt batch of cheese, and add the vinegar until it starts to lump.
Would love for you to post your recipe in the recipe section it sounds great. I have a pumpkin ricotta recipe that I was thinking I might add.