It works on the sub case not on the parent case.

I don't know the exact answer but I would consider using two detailed Pega traces, one for the 1 min example and one for the 25 minute example, and compare them to determine what parameters and what rules are involved for this setting. 

I think the change is in  your private check out , can you verify by check in the rule

I think you need to restart the cloud instance to apply the lock time changes . I used to change in the system variables lock time , that scenario you should restart the instance to apply the changes . Please try to restart and see check the changes are applied or not .

Both timings are getting set, but in different scenarios

1. When a user opens an assignment from a workbasket, 1 min is set as the lock timeout interval

2. In scenarios where Workbasket is not involved, like user creates a case, acquires lock on the first assignment in the flow, 25 mins is set as lock timeout interval.

version: 7.2 PE