It appears that there is an issue with the timeline block when using Next 7 days for assignment with group overrides dates.

Using https://qa.moodledemo.net/.
1. Use an existing course. Example: https://qa.moodledemo.net/course/view.php?id=2
2. Edit groups at https://qa.moodledemo.net/group/index.php?id=2
3. For Group A add student  Sally Student.
3. Go to course contents, and turn edit mode to On.
4. Add an assignment activity and use the following:
Name: CCC assignment
Allow submissions from 14 June 2023 00 00
Due date 15 June 2023 00 00
Cut-off date 16 June 2023 00 00
Common Module Settings / Group Mode = Separate groups.

5. Save and display.
6. Click More / overrides
7. Add a group override and use below GroupA:
Allow submissions from 25 June 2023 00 00
Due date 26 June 2023 00 00
Cut-off date 27 June 2023 00 00
8. Log in as the student user and visit your dashboard.
RESULT:
Timeline block shows:
Next 7 days
Thursday, 15 June 2023
00:00
Activity event
CCC assignment
Assignment is due · Activity examples

Change Next 7 days to Next 30 days
Timeline block shows:

Monday, 26 June 2023
00:00
Activity event
CCC assignment
Assignment is due · Activity examples

Change Next 30 days to All
Timeline block shows:
Monday, 26 June 2023
00:00
Activity event
CCC assignment
Assignment is due · Activity examples

As per results, the Next 7 days shows the default 15 June 2023 due date for the assignment CCC assignment. Changing it to Next 30 days shows the correct override date of 26 June 2023