Time to separate them?

Question
How do you tell the boys from the girls?  And how soon can they mate?
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The text above is a follow-up to ...

-----Question-----
Hi, On Feb 16th our little dwarf Russian gave birth to 5 little ones (bought her the day before supposedly not pregers!) they are now starting to fidget with one another.  They are eating & Drinking well.
Is it time to unload them on someone else?
-----Answer-----
At 3 weeks of age you can seperate. So this week you can seperate them. Friday will be 3 weeks so you only got a few days left. :)

Answer
Gennerally, they reach sexual maturity at 45 weeks of age. Here is a link on how to sex dwarf hamsters.
http://www.petwebsite.com/hamsters/sexing_hamsters.htm

You are going to have to hold the hamster by the scruff of the neck and look. Looking at the genitals there are two 'vents' - on the male these are the penile opening and the anus, and on the female these are the vagina and the anus. The gap between these two vents on the male is usually 1-2cm apart (Dwarf-Syrian) and on a female the gap is so small that it is difficult to distinguish the two separate vents.