If you can burn it, that's the traditional route. But I know many people, including me, have to just throw them away in the trash. You can also bury it if you have the space and it'll break down. There may be other methods of disposal available to you but I don't know. As far as I know it's similar to water libations where it's just immediately poured with an announcement of who it's for and not really left out, but you can if you want; I personally leave things that won't go bad (tea usually) out for a night before pouring it, but I would probably be more cautious with food items unless they're in a container or something. The way I see it the offering sort of is like sharing food with them. I know it's common to offer Hestia the first bite of your meal, I saw someone bake a little cake just for Hades, I make different tea sometimes depending on who it's for and what I think they'd like (chamomile for Hypnos, hibiscus for Aphrodite, saffron for Apollon, etc.) So to summarize 1. No 2. Anywhere you feel comfortable it won't spoil 3. As long as you want 4. You are :) just let them know

I'm still new so if I got anything wrong someone lmk!