Why wont Uxie appear?

Question

I go to the nameless cavern between 20h and 21h but it never appears.

Comments

Yay! You chose my answer!

Answer 1

-You might not have three Pokemon with max happiness on your team.
If you have changed your 3DS clock recently, timed based events (such as mirage spots) wont occur for 48 hours.
Other than that I don't know whats wrong.
Source (scroll down to uxie mesprit and azelf)