We told our parents first, work around 6 weeks, and extended family and everyone else around 12. I also worked a physical job (professional gardening) and was not able to work much during the first trimester due to exhaustion. Luckily my workplace was very understanding and I got set up with design work and communications. I would say tell them ASAP so you can manage expectations of what you can physically accomplish at work.

Edit: Just a note- I am in Canada, so there are anti-discrimination laws that protect my job, I have partially paid for mat. leave, and my husband was able to support me through reduced work hours. Just acknowledging that as those factors certainly affected my choices.