For some reason, when you take a nap, you go straight into REM. So you could try and WILD then. The only issue is, if you sleepy enough to fall asleep.

But at night, it's recommended you have prior sleep, at least 4.5 hours. The more sleep you have the better, because towards morning, your sleep cycle is mostly REM.

Some people claim they can WILD without prior sleep, but they are just few and far between. WILDing without prior sleep is something that yogis try to master for many years. It means, that you have to stay aware during first stages of sleep cycle, until you hit REM, (or first dream in NREM), and that can take as long as 80 min. (Sleep cycles are about 90 min long, first one is about 80 NREM and 10 REM).