What this measures
How many minutes your device scored you as asleep. It is time asleep as the device read it, not the hours you spent in bed.
How your device works it out
Movement and pulse are read together and the night is scored into asleep and awake stretches. Every provider scores that differently, and none of them can see what a sleep laboratory sees, so a quiet hour of reading in bed can be scored either way.
What generally moves it
When you went to bed and got up, shift work, travel, alcohol, small children, a device that was charging for part of the night, and a nap the provider did or did not count.
Why Thriverence shows it
Sleep is the input most members can act on directly, so Readiness weighs it and the screen shows it as a trend against your own usual nights rather than against an eight-hour target.
What it is not
This is not a sleep study and it does not identify a sleep disorder. The figure is an estimate from a consumer device, it is not a diagnosis of anything, and a run of short nights is not a finding about your health. If your sleep is worrying you, the resources below list people who can help.