I sent a LINE message to Koichi and he replied to me in a second. That made me chuckle.
When I go to bed, I usually fall asleep in three seconds.
Your pronunciation can reach native-level in just twelve seconds.
The kanji and the word are exactly the same. That means they share meanings as well - that is the unit of time, second.
The reading is the same as you learned with the kanji. It's presumably because it's usually attached to other things, like numbers, making it act more like a jukugo word would. Anyway, you should only need a second to learn this reading, since you should already know it.