When switching to 6am, 90% of time fps will drop from 60fps to 30fps things will get back to normal after a while.

Configuration:
OS:win10 up to date
Driver up to date
Resolution used:1920*1200
cpu:i7 920 @ 3.7ghz
gpu: gigabyte gtx1080 8go Gpu@1962Mhz Ram@10010mhz
ram:DDR3 1600 Mhz triple channel 12Go
storage:ssd Crucial 1To

Ingame graphic setting everything maxed out beside
"Terrain draw distance" = high
TAA instead of MSAA