I was thinking it might be nice to vary a flow by time of day.. so between 11am and 2pm it would say one thing, and otherwise it'd say another thing.

I didn't see any way to assign dates/times to a variable so that they can be used in a conditional statement later on. You'd want to keep it quite generic, so I can say something like;

Variable name: HOUR

Initial value: {dateFormat(new Date(), "h")}

This is quite flexible, allowing developers to do what they need to do with the date/time in their Flows.