When working on JDK-8190353 I realized that the verification code doesn't include time possibly spent balancing queues. This is likely because this has not been done in the past since the Full GC hasn't done parallel reference processing. That will not be true once JEP-307 is completed, here is an example when using parallel threads:
[0,379s][debug][gc,phases,ref ] GC(13) Reference Processing: 41,8ms
[0,379s][debug][gc,phases,ref ] GC(13) SoftReference: 41,7ms
[0,379s][debug][gc,phases,ref ] GC(13) Balance queues: 0,6ms
[0,379s][debug][gc,phases,ref ] GC(13) Phase1: 14,3ms
[0,379s][debug][gc,phases,ref ] GC(13) Phase2: 13,4ms
[0,379s][debug][gc,phases,ref ] GC(13) Phase3: 13,4ms
[0,379s][debug][gc,phases,ref ] GC(13) Discovered: 457511
[0,379s][debug][gc,phases,ref ] GC(13) Cleared: 0

Adding the balance queue time should be fairly straight forward, using the same mechanism as for the other phases.