This problem with high ping at prime time (6pm to 10pm) started about 1 week ago for me, even tho many people complain about this. Most of the informations you can find in video (with timestamps).
TLDR is: I tested at least 5 other online games and problems i have during prime time is in ESO. I tested on two different pc's on same network.
I did pathping and tracert. I found out that i reach their servers in Germany with around 30ms but after going through their 3 different IP's my ping ends up on 130ms in cmd (180ingame).
In video you can see 3 games live tested during prime time (at exact time i have high ping in eso) while constantly pinging their EU servers in cmd.
Here is video link:
https://youtu.be/0UdwqrBUi8M