No bro, I guess you are new. It is always like that. Arena 3v3 last 2 week cycles but ends one day before 2nd week cycle. You wrote it yourself . Till Mar 9th 5:00 AM (Sever time obviously ) So how can you play it Mar 9th after 5:00 AM server time ?

It is not problem what they wrote, it is problem how you perceive this information. You perceive it as 9th is inclusive. But it is exclusive. You could see that from new events cycle, they apply same logic on other events. I would not told you that if there was no 5:00 AM information, but there is so thing is clear.