A millennium in days (Something "in" terms of another thing, for instance, "Thirty feet in meters")
Тысячелетие в днях.

A millennium of days
Sounds like nonsense. First translation that comes in mind is name of topic. But maybe context is important.

Also жду не дождусь. What are the exact connotations to the phrase and can you say Ждал не дождался тебя
Дождаться is perfect form of "ждать", which means something like "to compete waiting with positive result".
So, direct translation could be "I am waiting, but (probably) I will fail to complete this waiting". Second part looks like lack of enthusiasm, but in reality it is shortened "не могу дождаться" (cannot wait any longer). So, this part serves as enforcer and whole meaning is "to wait with strong desire".
But if you put phrase in past form (Ждал не дождался тебя) it becomes simple fact that you failed in waiting. So, it has no sense. You should use this idiom while first part is in present and second part is in future.