You can do either. WILDs at the start of the night are very tough to learn. I can WILD at the start of the night, but I usually only do it when I am in the mood, because it takes a bit longer to generate and the dreams never last long.

WILD after waking up. It is easy as hell by comparison and the dreams last forever. There is really no reason to learn to WILD at the start of the night unless you want concentration training.