How long can this stay at room temp?
I would keep this refrigerated whenever you're not serving or eating it since it has ricotta in it. Before serving I would let it come to room temp for about 30 minutes. In terms of leaving it out in general I wouldn't go past the 2 hr mark. You're probably not in danger of it spoiling, but better to be safe with dairy.
A found this on an Italian Cooking website, which features a similar recipe: "Ricotta cake will keep at room temperature well wrapped for two days, but if you are keeping it longer, or if your kitchen is warm I'd store it in the refrigerator. "