In The Sandman - Overture #5 we learn that
Dream is a son of Night and Time,
two entities who were not seen before (in the original run). If there was any doubt that Night and Time are the parents of all the Endless, this post by Neil Gaiman lifts them.
On the other hand, it makes one wonder - why Night and Time? Of all possible entities (or of all possible names), why those two?
Time is described as "watch[ing them] from the micro-moments between seconds", while Night is described as "exist[ing] in the vast stretches of untime and unspace beyond every event horizon". What can we learn about the Endless from their parentage? What symbolism, if any, does it carry?
The part about Time is particularly interesting; Time and Night would have to represent some fundamental forces or events, given they're the parents of such fundamental things as the Endless. However, time was described as non-essential or "bendy", in some regions of space, and especially in Dream's realm, in soft places. It wasn't treated as very important, so it seems a bit odd that the entity who fathered Dream is Time.