function getEpoch(epoch) {
				if (!epoch) {
					return 0;
				}
				if (typeof epoch.getTime === "function") {
					return epoch.getTime();
				}
				if (typeof epoch === "number") {
					return epoch;
				}
				throw new TypeError("now should be milliseconds since UNIX epoch");
			}
Used to grok the `now` parameter to createClock.

@param {Date|number} epoch the system time
@returns {number}