If you are talking about weekends, Sundays especially, it seems that many people have that day off around the world. Let me also say this, it is very likely that many of these people are at coffee shops or on social media colluding. It's not unusual to see suspicious behavior such as preflop 3-4 betting then checkdowns, extra time taken by these players while in hands with each other (the lag is due to communication between them), softplay. Obviously if you know more of the dead cards, your math becomes more pure.
Just to be clear, I am definitely NOT saying every player from Eastern Europe is colluding or that such collusion is limited to that area, I am merely saying that Sundays are the days I see the most suspicious activity. The good news is that generally speaking, cheaters have to cheat because they aren't that great, so you can beat them with traps and unconventional play.