CAB Date Restrictions and CAB Cutoff Validation for Normal Changes

[Sirri]

Hi Team,
I have a requirement on the Change Request [change_request] table for the CAB Date/Time (cab_date_time) field and would appreciate guidance on the recommended approach and complete implementation scripts.
Scope
This requirement applies only to Normal Changes.
CAB meetings are conducted on:

Monday
Thursday

Requirement 1: Restrict CAB Date Selection
For ITIL fulfillers, the system should allow selection of CAB Date/Time only for CAB meeting days:

Monday
Thursday

If the user selects any other day, the system should:

Display an error message.
Clear the value from the cab_date_time field.

Examples

Selected Day - Expected Result
Monday - Allowed
Thursday - Allowed
Tuesday -Not Allowed
Wednesday -Not Allowedx
Friday -Not Allowed
Saturday -Not Allowed
Sunday- -Not Allowed

Requirement 2: CAB Cutoff Validation
A cutoff time exists for including changes in the upcoming CAB meeting.
Monday CAB

CAB meeting day: Monday
Cutoff time: Sunday at 16:00

If an ITIL fulfiller attempts to select a Monday CAB Date/Time after Sunday 16:00, the system should:

Display the following error message:

Time to include a change in CAB has passed, please follow CAB Cutoff exception procedure

Clear the value from the cab_date_time field.

Thursday CAB

CAB meeting day: Thursday
Cutoff time: Wednesday at 16:00

If an ITIL fulfiller attempts to select a Thursday CAB Date/Time after Wednesday 16:00, the system should:

Display the following error message:

Time to include a change in CAB has passed, please follow CAB Cutoff exception procedure

Clear the value from the cab_date_time field.

Exception
Users with the change_manager role should be exempt from both validations.
A user with the change_manager role should be able to:

Select any CAB date.
Select CAB dates after the cutoff time.
Proceed without receiving any validation error.

Configurability Requirement
The solution should use System Properties so that future CAB schedule changes can be managed without code modifications.
Suggested Properties
CAB Meeting Days
Monday,Thursday
or
1,4
CAB Cutoff Time
16:00

Questions

What would be the recommended technical approach for this requirement?

onChange Client Script
GlideAjax + Script Include
Business Rule
Combination of Client-side and Server-side validations

How would you implement the solution using System Properties for:

CAB meeting days
CAB cutoff time

Has anyone implemented a similar CAB validation requirement?

Could someone please provide the complete implementation, including:

System Properties
Client Script
Script Include
Business Rule
Sample code/scripts

Any guidance would be greatly appreciated.
Thank you.