Yes, you can WILD right away.

The reason that people say to do if after a few hours of sleep is that your REM periods will be longer and closer together after you sleep for a few hours, and on top of that being a bit tired and groggy will ensure that you're 'sufficiently' tired.

That being said it is possible to WILD immediately, you can lucid dream outside of REM periods, and REM periods can also occur immediately when you first go to bed for the night.

So really, just read, try out what you like the sound of, and experiment.