That one is often confusing becuase of the way it has been written.
The pump should move immediately as the throttle rotates off of slow idle.
The 'clearance' is when the throttle is full wide open there should be travel remaining before the spring bottoms out . In other words with the throttle wide open, a feeler gage can be forced in between the lever and the adjuster.
18* at what rpm? This is the key.
yes it may end up being too much at 2400 rpm to use vac advance, or way too much at high rpm and wide open throttle. Its under heavy load, like wide open throttle 2 and 3 rd gear that too much timing advance can be really destructive. But unless you need to go racing, work on idle and then off idle. You can even drive it around the block at light and moderate throttle.