We were 7 weeks through to about 12 with telling people. There is no right or wrong, its all about what you feel comfortable with.
My SIL tried to tell me last night that I had done it wrong, and I shut her up by saying - it worked for me, doesn't mean it had to work for you!!
Just do what feels right - you might make a couple of mistakes here or there, but really, its happy news so there is no harm!
Good luck,
Fi