Can I order a cappuccino after 11am?

You can, they'll serve it, and no one will be rude to you — but no Italian is doing it. Milky coffee is considered a breakfast thing, heavy on the stomach after a real meal, so after lunch or dinner Italians drink an espresso. This is a soft custom, not a rule, and the idea that you'll be shamed is mostly an internet invention. If you want a cappuccino at 3pm, have one. If you want to order like a local: caffè after meals, cappuccino before 11 with a pastry, and never a cappuccino to finish dinner.