Hi handyfish,
It takes approx. 28 days.
Honestly, I don't count. I just estimate in terms of weeks.
I leave plenty of floating plants on the surface of the water. The fry will hide in them.
When I believe she will pop soon, I will look out for fry everyday. When they finally arrive, I fish them out and transfer them to my spare tank. U can also use a breeding net.
DIY is cheap & good.
As she nears the time to give birth, the pregnant mother will become extremely bloated. Where her anal fin is, it will spot a white little thing. She will also get chased around a lot more.
FYI:
Pregnant or just fat?