Word meaning "before sleeping"
Just as post + prandial [of or relating to a meal (as dinner)] means "after dinner," so pre + somnial [of or relating to sleep or dreams] can mean "before sleep" or "before bedtime."
So: pre-somnial.
"But I was not yet able to trace my day-dreams back in the morning, as I did those of the pre-somnial state." [J. Varendonck, The psychology of day-dreams]
Bedtime, or is that too childish?