1 whole year should have passed on the wealth
Even after one has wealth that meets the prescribed criterion for Zakaat, it is necessary that 1 complete year should have passed on it. This condition shows the ease and convenience of the system of Zakaat.
All the Jurists are in consensus about this. An explicit command is present about. There is a Hadith in Sunan Ibn Majah:
Translation: It is narrated on the authority of Hadhrat Ummul Momineen Hadhrat ‘Aisha (May Allah be well pleased with her), she says: I heard the Holy Prophet (Sallallahu alaihi wa sallam) say: There is no Zakaat on wealth unless 1 year has passed on it. (Sunan Ibn Majah, Hadith No. 1864)
As mentioned in Al Bahr Ur Raaiq, Vol. 2, Pg. No. 356.