Congrats on your BFP! I'll tell work after my 12 week scan. I have a physically easy office based job and really flexible hours. I can work from home wherever I want and am usually only in the office 3 days a week. So no real need for anyone to know before then.
My first pregnancy I had a real sense I shouldn't work up until the end. I knew I'd be earlier rather than later. My last day was 36+5 and my daughter was born exactly a week later at 37+5. This time I don't plan to go into the office past 35+0 and will work from home instead. I have a really long commute (3 hours and 10 minutes each way on the days I'm in the office, which is why I'm not there every day). I don't want to be making that trip past 35 weeks. But I also don't want to stop work early either as I do want to actually use my maternity leave (I get a full year) for once baby arrives. Depending on how busy I am and how I feel, I'll probably work til 36 weeks or even 37. My job is project based and there's no maternity cover so what doesn't get finished before I leave just won't get finished and if we don't meet certain deadlines, I won't have a job to come back to as my role is totally externally funded. So it's in my best interest to get as much done as I can so I can enjoy my time off and relax. But I'll probably stop by 37 weeks at the latest.