Lecithin is fine as a source of choline (if you take enough of it, because there is a lot of other stuff in it besides choline). I've had success with it both before bedtime, and at WBTB-time. But remember that it does have to work its way through the stomach, which - even if it is mostly empty at the time - will take at least 15 minutes, or so.

Ginkgo I take only at WBTB-time, but it is rather stimulating so there is some risk of not falling asleep so quickly again (can of course be mitigated with sleeping aids).

Be aware that there are many separate aspects to lucid dreaming, and different supplements/herbs may be effective in some respects, but not in others. So, for example, you might distinguish between dream vividness, dream stability, amount of dream time, lucidity, dream story line complexity, memory.