1. conjunction /ʍɛn,wɛn,ʍɛn/
They were told when to sleep.
b) At such time as.
I’m happiest when I’m working.
2. pronoun /ʍɛn,wɛn,ʍɛn/
What time; which time
Since when do I need your permission?
3. noun /ʍɛn,wɛn,ʍɛn/
The time.
A good article will cover the who, the what, the when, the where, the why and the how.
Wikipedia foundation.