How To Set the Number of Days to Reflect Age Differences

"NRowe;c-18145034" wrote:
I play with a custom age span for each stage where seven days = one year. Pregnancy is extended to four days (and often goes for five). University takes a minimum of three years.

Seasons are seven days, which doesn’t truly fit, but I make it work. There holidays are set so that approximately two days is a month.

So the answer to your question would depend how far apart in age they were. Seven days to a year. If they were three years apart (like my RL brother and I), approx 21 days.
I just read that your Sims are one year apart. So anything from five to nine days.

I play on Long, but really barely had a baby born, when another one was on the way. LOL I know, I know. I really was more careful with the iteration of Erik Cantrell in one of the saves prior to the one I'm playing now. Oi! Pregnancy in my game is still three days. Babies are babies for six days. I would have to go into MCCC knowing exactly how long each life stage is, and adjust things while in Normal, then switch to Long. (I think that's how we're supposed to do it.) I know we can't adjust while on Long. Tried it and it doesn't work, so I have just left it to Long. I wish they had given us EPIC. I used that setting in Sims3, adjusting the length for each life style below Teen. I know I gave my YAs a bit more time and if memory serves I added time to the Elders.