In quran,
(1) An year has 12 months (Sura 9:36)
(2) Breast feeding is compulsory for 2 years
(24 months)(Sura 2:233,31:14)
(3) Combined time for Pregnancy and breastfeeding is 30 months (Sura 46:15)
the period of pregnancy for human beings is 6 months (25 weeks), isn't?.

Wikipedia says "The earliest gestational age at which the infant has at least a 50% chance of survival is referred to as the limit of viability. As NICU care has improved over the last 40 years, viability has reduced to approximately 24 weeks,[65][66] although rare survivors have been documented as early as 21 weeks.[3] "

Besides there is no word 'minimum' in 46:15 as it talks about a child born to its parents normally.
If you disagree with me, please feel free to scrap/note/text/comment me...