Not returning to work

I’m 17 weeks pregnant. My husband and I recently talked about after I give birth to the second that I not return to work. I’m due February 7th so I plan on not coming back after New Year’s eve so my last day of work would be December 31st. My question is when is a good time to let my work know when I’m taking my maternity leave and that I will not be returning. My work also does not offer any kind of benefits, insurance, vacation days, FMLA etc. I work as an MA at a doctors office and we’re only open 4 days a week and I work 3 MAYBE 4 days and only about 20-25 hours a week so not even full time. I’ve been there as a paid employee since May.