Hey there, Richard Tai
Have you submitted feedback to the Microsoft Family Safety team?
To submit feedback to the Microsoft Family Safety team, please sign into your account here: https://account.microsoft.com/family/home
Once you have signed into your account, please click onto "Feedback" at the bottom of the page
You can then complete the feedback form to submit feedback directly to that product group.
The team can then look at your feedback and take it onboard. When submitting feedback, I generally tick the box that says "You can contact me about this feedback". This allows the team to contact you if they have anymore questions.
In terms with how the timer counts down. I want to say, from past experience, it counts down regardless if you have locked the PC or not. This is because the PC still counts it as an 'Active' session, even if it is Idle. It would be just like you walking away from the PC without locking it.
With regards to sleeping and hibernating your PC. I suspect it would count this as an inactive session due to the PC having to put it's self in a low powered state. So I suspect this wouldn't count. However, to be sure, I would have to ask about this. However, in order to ask, I would need to dig out the email address I used last time to contact that product group providing I still have it.
Hope this helps,
Nathan