How long does it take after treatment for breast cancer to metastasize to other parts of the body?

Hopefully never: Hard to tell you specifics without much more detailed information on type, size, stage of the breast cancer. Of course the hope is that treated breast cancer does not metastasize. Most cancers are thought to have a lower chance of returning or spreading after 5 years from the successful treatment phase. But every person is different and close medical oncology follow up is recommended.

It varies a lot: Most breast cancers are successfully treated and cured with modern treatments. There is of course some risk of relapse or recurrence of cancer. The recurrences mostly occur during the first 2-3 years after primary treatment but can take up to 5 or even 10 years to come back as metastases. So you need to have check ups and follow ups with your doctors for rest of your life...At least for 10 years.