How do I say 'later'?

等一下 is your everyday “hang on a sec” — add it before any request for patience. The 一下 softens 等 from a command (“wait!”) to a request (“wait a moment”). Without it, a bare 等！sounds abrupt.

以后 operates differently from English “later.” It means “after” and can attach to events: 吃完饭以后 (after eating), 毕业以后 (after graduation). As a standalone, 以后再说 is the classic deferral — it pushes something to an unspecified future time, and whether it actually comes back depends on the relationship.

回头 deserves special attention. On the surface it means “later,” but it has earned a cultural reputation as the word people use when they have no real intention of following through. 回头请你吃饭 is the Chinese equivalent of “let’s do lunch sometime” — warm in tone, zero in commitment. Context and relationship tell you which one it is.