Very little operates between those hours (I was surprised to find any, there used to be an absolute bar on peak hour freight on the SR suburban lines ).Or, you just make sure freight operates or is induced to operate at off-peak periods. Considering how full the Southeastern is, which feeds almost all of the WLL traffic, it would be beneficial for all concerned for little more than a standard half-hourly path to be available throughout a period of about 07:00 - 09:59 and 16:00 - 18:59. That can be from Hither Green or Shortlands, and timed identically between Nunhead and Mitre Bridge.
Anyway, back to frequencies:
12tph on the NLL should be doable, 4 Richmond/8 CLJ (query: does the reduction in Richmond capacity work?); add 2 SN and you still have 2 freight paths on the WLL.
the significant issue is platform 1 at CLJ which couldn't accommodate 8tph at alternating 5/10min intervals.
Really clever timetabling could have 6tph at each platforms shared by WLL and SLL (Mildmay and Windrush?) but "performance risk" springs to the lip.... or an expensive reinstatement of the old P1 viaduct.
Or you could divert 4tph via Longhedge towards Dalston Jn, thus giving the SLL 8tph.