3x acceleration of plotting. I'm not complaining, but why?

[Keeermalec]

Phase 1/4 on queue 2/13
Time for phase 1 = 28290.768 seconds. CPU (47.560%) Sat May 22 21:08:01 2021
Time for phase 1 = 16786.905 seconds. CPU (85.420%) Sun May 23 09:31:34 2021
Time for phase 1 = 10405.255 seconds. CPU (141.480%) Sun May 23 18:25:58 2021
Time for phase 1 = 10617.535 seconds. CPU (142.210%) Mon May 24 01:27:27 2021
Time for phase 1 = 9931.942 seconds. CPU (143.210%) Mon May 24 08:08:02 2021

Ryzen 9 3900 X
128 GB RAM
Primary temp disks: Kingston SA2000M8100 1 TB NVME SSD + CRUCIAL CT2000P1SSD8 2 TB NVME SSD
Secondary temp disk: Samsung SSD 860 QVO 2TB SATA SSD

4 queues on Kingston SSD
13 queues on Crucial SSD
Staggered every 30 minutes

What's with the shortened phase 1s and increased CPU loads each new plot?