Can I run happy-hour pricing on drinks?

Yes — Settings → Upsells & offers, rule type "Happy hour / day-part offer": pick the item, the days and the hours. Outside the window the normal price returns automatically, so nobody has to remember to switch anything back. Worth knowing: days and hours can be set on ANY of the rule types, so you can time-limit a pairing or a bundle too — that rule type exists for offers that are purely about timing.