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.
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.