How much gestation does the Breeder perk shave off with Short Pregnancy disabled?

[CourtOfTheGrayWaves]

I ain't none too good at reading the fancy math on the wiki.

 

[SmithEK]

I ain't none too good at reading the fancy math on the wiki.

You can get shorter pregnancies by going to Evergreen.

 

[beta048596]

I ain't none too good at reading the fancy math on the wiki.

It increases pregnancy speed to 1.5 (from 1), so it will take 33% less time.
As @Emily Smith said, this is only for the start of the game, when you reach Evergreen she can increase the speed by 1 up to a limit of 8 and possibly more if you have the perk Corrupted Breeder.