Perceived Health Study:

https://psycnet.apa.org/record/2017-31316-001

Sleep regularity more important than total time:

https://pubmed.ncbi.nlm.nih.gov/37738616/

Wearable devices research (Aura, Whoop, Apple Watch):

https://pubmed.ncbi.nlm.nih.gov/36016077/

https://pubmed.ncbi.nlm.nih.gov/34201861/