drop speed only refers to how long the delay will be before Cetera moves to the next index inside the drop menu:
1. Gem of Nulgath
[wait 1000ms/1 second]
2. Essence of Nulgath
[wait 1000ms/1 second]
3. Diamond of Nulgath
[wait 1000ms/1 second]
Also note, it is wise to always keep your drop speed At or ABOVE 1000ms, otherwise the servers will see that you're making requests with an abnormally low delay between each request; this is how a lot of individuals get caught and 'reprimanded' by AE.