Bad ping at night

I'm playing at Singapore/Japan server (Malaysia GMT+8). At first, I thought at night time, a lot people started playing after they come back from work or something, that's why is lag. But, is the same in the weekends, the whole day is fine, when it reaches 7pm; my ping just sky rockets. Previous patch, this did not happen. I can load youtube and watch stream fine. Only mapping have this issue, crafting and everything is fine. I tried change my 3d cache to 100gb, that does not seem to fix it, is like the server just plummets at night from 7pm to 12am. It's really frustrating.... I can just stop playing at night i guess...