Maternity leave

When is a good time for maternity leave ? Or to even announce that I’m pregnant? I start a new job soon . I have orientation Wednesday but I’m not telling them I’m pregnant. I’m pretty sure it’s obvious. I’m 6 months pregnant so I’ll be only working for 3 months (I plan on working until I go into labor) but I feel so bad that I’m only working for 3 months then will be leaving for 2 months . (I will be a caregiver at this job)