Welcome @ange32004, From what I've read most CPAP machines reset at noon so record from 12:00 noon until 12:00 noon the next day.

"The Day Resets During your Usage:
For most CPAP machines, the day resets at noon. This is because most people sleep at night. However, many of our CPAP customers work at night and sleep during the day. This can cause part of your CPAP usage to go on two separate days. This will dramatically throw off the time you think you are going to see on your CPAP report. The easiest resolution for this is to contact your provider to have the day cutoff changed for you. Rest assured that the time will be counted, but it may be on two separate days."
-- Usage Hours don’t add up on your CPAP – What is Happening?:
https://cpapmyway.com/blog/missing-time-on-cpap-compliance-report
Are you having concerns about CPAP compliance?