It's all true what is said in above posts.

But, WBTB is not required for a DILD. You do all your mental prep during day and as you falling asleep. If you happen to wake up at night for whatever reason, you can sit up, do a few RCs and mantras, set your intent and go back to sleep with your mantra.

But a regular WBTB is not required as it is for WILDs. It wakes up your mind enough, so you don't fall asleep right away and you are able to wait for a dream to start before falling asleep again. But for a DILD, there is no need for this, as you fall asleep first, then you get lucid when already in a regular dream.