Date Comparison is not working correctly

I am assuming Timestamp precision mismatch - database records include seconds/milliseconds but your cutoff time is exactly 7:59:00, causing records like 7:59:30 PM to incorrectly fall into "After 7:59 PM".

 Use 8:00 PM as your cutoff instead of 7:59 PM, and use < and >= operators instead of <= and >. 

Update your NWS_SlaCutOffTime() rule:

/* Use 8:00 PM for cleaner boundary logic */
datetime(
  year(today()),
  month(today()),
  day(today()),
  20, 0, 0
)

a!recordFilterList(
  name: "SLA Due Date",
  options: {
    a!recordFilterListOption(
      id: "before",
      name: "Before or at 7:59 PM Today", 
      filter: a!queryFilter(
        field: 'recordType!{ee5aa46d-0228-430f-a794-1134a11fbcc0}CMGT_Task.fields.{56f4ac00-4b4b-4c1b-b841-1938bd23ac80}dueOn',
        operator: "<",
        value: rule!NWS_SlaCutOffTime()
      )
    ),
    a!recordFilterListOption(
      id: "after", 
      name: "After 7:59 PM Today",
      filter: a!queryFilter(
        field: 'recordType!{ee5aa46d-0228-430f-a794-1134a11fbcc0}CMGT_Task.fields.{56f4ac00-4b4b-4c1b-b841-1938bd23ac80}dueOn',
        operator: ">=", 
        value: rule!NWS_SlaCutOffTime()
      )
    )
  },
  allowMultipleSelections: false
)

I also agree with this, but as OP did not really specify what they meant by "not working", it's hard to know whether this is even vaguely the direction of their issue.  But this is good general guidance for implementing timestamp-based filters.

True, without seeing the actual behavior it's hard to pinpoint the exact issue. The timestamp precision and timezone considerations are the most common culprits for date/time filter problems, so starting with these solutions usually resolves most cases.

True, without seeing the actual behavior it's hard to pinpoint the exact issue. The timestamp precision and timezone considerations are the most common culprits for date/time filter problems, so starting with these solutions usually resolves most cases.