Ops.....Trying to start a new discussion, after typing in the title, your (this) post auto pops up.
Cannot believe over 4 years this situation has not changed yet.
My situation is:
I set 1am-9am as bed/wake up time.
Then after wake up at 10am, I changed the bed / wake up time to 1pm-4pm.
But the 1-4pm sleep is not identified as "Sleep".
But it's interesting that I set Pulse Ox monitor in "Sleep", then the Pulse Ox is recorded in 1pm-4pm as well.
Which means, seems the watch know it's a "sleep" time slot in 1-4pm (so it monitors the Pulse Ox), but APP does not identify it in same day, so the afternoon one is not marked as "sleep" time slot. (seems allow only 1 sleep session daily).