Well it takes about 6 weeks in total, looking at the wiki page you can check out info about this and a walkthrough about most of the routes. On pregnancy:
" One week after the fertilization, the announcement is made and the main character may have to convince the mother to keep the child using
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. From then on, this event lasts 6 weeks during which the progress of some routes is paused. The gestation evolves over 4 weeks with three different stages until another message informs about the birth. Newborns can be a boy, a girl, or twins of opposite sexes - this choice being random but restricted by who is the pregnant character. The mother and the baby may stay inside the hospital a few days. Another 2 weeks pass until the baby is sent to daycare and normal activities are resumed. Related dialogues and scenes are present throughout the maternity. "
So in short after they are pregnant, it takes about 4 weeks until they give birth, upon which you get a message about it, then it takes 2 weeks before the kid is sent to daycare.
On Maria once she is pregnant she and tony would have let you know then it as mentioned takes 4 weeks before she gives birth.
You should have noticed her getting a big belly however and Maria is one of the characters you can sleep with while she's pregnant. If you go to the pizzera and enter the kitchen you'll notice her standing there fully pregnant going with a naked apron look if you talk to her you can engage in sex right there.
