Is the two-year breastfeeding period calculated by the Hijri or Gregorian calendar to determine the weaning time?

The year recognized by Islamic law (Sharia) is the lunar year, based on the Almighty's saying: ﴿Indeed, the number of months with Allah is twelve months in the Register of Allah, the day He created the heavens and the earth; of these, four are sacred. That is the correct religion.﴾ [At-Tawbah:36], and His saying concerning the crescents: ﴿They ask you, [O Muhammad], about the new moons. Say, "They are measurements of time for the people and for Hajj."﴾ [Al-Baqarah:189]. And the new moons are appointed times for people.

Regarding breastfeeding, it is permissible to wean before two years if both parents consult and agree for a [valid] interest, based on the Almighty's saying: ﴿And mothers shall breastfeed their children for two full years, for him who wishes to complete the nursing.﴾ [Al-Baqarah:233]. Accordingly, the girl can be weaned on October 8, 2008, corresponding to Shawwal 7, 1429 A.H.