WotLK Lag

[headhunter230]

Greetings, past week i have unusual lag (1-2sec delays while moving or casting spells and its perriodically (feeling it even worse on battlegrounds)) The interesting part is that my ms is not higher than 80 MS. I can feel that on all realms. My internet is completely fine (doing speed tests wich are : 21ping ms) Tested on another games and there is no any lag or delay. I also took care to be sure that there are no external devices connected to my wi-fi, wich could consume some of my net. i also turned Wlan off, and switched to ethernet cable plugged straight into laptop. And there are no any programs runnning in the background at all. Durning daytime everything is perfect. The lag usually occurs at 4pm ST or something like that, and it presists untill i go to bed wich is 10 pm ST. i also tried to delete wow ceche folder. I presume it has something to do with the server population durning that time, because a lot of players come to play after work, but still does not make sense, because this is happening since 1 week. I had never felt such difficulties at any time in general. My gaming experience on this server was always smooth, no problems at all. But it is what it is now, cannot be unseen. I tired to use the "report lag" from the in-game Request help, then i opened a short ticket of explaining. But the answer was not satisfying due to the lack of solution and actions. So once again i seek help, this time on fourm. Would really appriciate any kind of support or direction of how to determinate this problem. Cause its getting on my nerves, cant enjoy my playtime at night. Just to mention that im from Bulgaria. I appeal any GM to help.
Thank you.