How do SLA, DueBy Time and Overdue status interact?

Hello,
I have a few questions about the SLAs, the Dueby time and the Overdue status.
From what I think I understood, the SLAs determine the Overdue Status. I do not understand the functioning and the role of the Dueby Time.

Let us say, the SLA has a resolution time of 4 hours and the ticket is created at 09:00.
The DueBy Time is set at 13:00.
At 10:00, the ticket is set On Hold.

Let us say, is is now 14:00.
From what I can see in SCP, the DueBy time is still at 13:00.
The Overdue Status is false.

Questions:
1. Is the DueBy time ever updated automatically? Or is it computed at ticket creation time and then remains at the same value?
2. Does the Overdue Status take the value from DueBy time into account? Or is the Overdue Status exclusively determined from the SLA and the timer being running or stopped (that depend on the statuses Open, In work, On Hold)?
3. What happens to the Overdue Status when I modify the DueBy Time?
4. What effects does changing the DueBy Time have?

Thank you for clarification.
Susanne