on pokemon how do i do a night time happiness evolution

[tan]

how do i do a night time happiness evolution on pokemon

[Zidarose]

The key to it is the timing of when the Pokemon gains a level at the appropriate level of happiness.

As for getting the right amount of happiness, I would suggest reading this guide:
Pokemon Platinum Happiness Guide

The second part is actively using the Pokemon between the hours of 8pm and 4am. They need to gain a level and the evolution sequence should automatically begin. If the Pokemon tries to evolve before this time, hit "B" during the evolution sequence, to cancel the evolution.