Why does Health App on my iPhone show the graph from 6 PM to 6 PM?

[eketat4563]

So I bought an Apple Watch S4 Nike+ a few days ago and then tried a couple of sleep tracking apps (Pillow, Sleep++, Autosleep) and decided to settle for Autosleep because it worked the best of the three. I took a nap today evening for about an hour from 5:30 PM to 6:30 PM and for some reason, Sleep Analysis in Health App on my iPhone (running iOS 12.1) registered half of that for today and the other half for tomorrow. The same thing happened yesterday as well. Whichever view it is, Day, Week or Month, the given graph shows data from 6 PM to 6 PM. I was on a call with the local Apple team and they were of no help. I looked around the internet for a way to change it to 12 AM to 12 AM or some other time period but found nothing really helpful. I found an Apple Discussions page where another user had this problem after travelling to another country, and thus another timezone, but for me, that never happened.
What about you guys? What does the Health app's Sleep Analysis show on your iPhones? Anything which anyone can suggest?

 

[Tartarus]

Open AutoSleep on your iPhone, go to Settings > Wizzard and follow the instructions.

 

[doogald]

Open AutoSleep on your iPhone, go to Settings > Wizzard and follow the instructions.

Yes. To expand - one of the questions asked by the wizard is what time that you usually go to bed (mine is set to 10 pm, I believe, though I usually go to bed at 11.) Any sleep that happens before that hour counts toward the previous day, anything after that hour to the next day.

See howdoitracksleep - AutoSleep