Usually a bedtime spanking is announced well ahead of bedtime. For example, a child that misbehaves in the afternoon is given one spanking right away and is informed it will get another spanking at bedtime, as a "reminder". The bedtime spanking will often be milder than the main spanking. In cases when the main spanking was given with an implement such as a hairbrush, the bedtime spanking is often only a short hand-spanking, just to refresh the effects of the previous spanking and the memory of it.
Bedtime spankings come with more relaxed and personal connotations than daytime spankings because of the setting (often, in the child's bedroom) and dress (often, barefoot and in sleepwear such as nightshirts or pajamas). Usually the child will be told to get ready for bed, so everything that needs to be done is done. The child may also be given a bath before. Common positions for bedtime spankings are OTK (and its variants), lying on the bed, the side-of-bed position, and the diaper position.
After the bedtime spanking, the child is usually hugged and reassured, then tucked into bed, letting them cry themselves to sleep if necessary. If the spanking was hard (as in some stories), the spankee may need to sleep on their tummy.
In Rejuve Universe
Here is an example of bedtime spanking in a spanking comic:
Bedtime spanking comic by Barbossasdaughter (2009), part 1
Bedtime spanking comic by Barbossasdaughter (2009), part 2