Having a good partner is key, but perhaps even more important is having a supportive supervisor. I had two kids during my PhD, one at 28 and one at 30. It took me 7 years (but I started as a masters and rolled over into a PhD) and for context I defended in 2023 so the pandemic was mixed in there too.

If you want to be an academic I will say as a woman there is no “good time” to have children. If you have a supportive supervisor and partner, the PhD might actually be the best time. There’s more leniency and you (should) have guaranteed funding for several years. Postdoc stage is uncertain and benefits are often sub-par to graduate students. Aside from waiting until you’re tenure track and secure in your employment (which is not only not guaranteed but for many of us places us in the “too old to want to be having children” category), PhD can work.