For new papers I think it would be appropriate when the paper gets sent out for peer review (as anyone can submit a paper anywhere but a journal sending it out to reviewers at least meets initial journal standards/QC). It will take 1-2 months to receive revision comments and even longer to submit revisions before being possibly accepted. As this process may take a year, I think it's worthwhile to at least let the Adcoms know you have something in the pipeline.
For a paper that's under review/ in revision that you might have mentioned in the primary or secondary, I think it is appropriate to update after acceptance.