‘Umrah of Ramadan starts at sunset of the last day of Sha‘baan
20-1-2014 | IslamWeb
Question:
I want to travel to perform ‘Umrah. Is it valid to perform it in the first night of Ramadhaan after 12:00 am?
Answer:
All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The month of Sha‘baan ends with the appearance of the new moon of the month of Ramadan. Performing ‘Umrah on the night when the new moon of Ramadan appears is included in the meaning of the Hadeeth narrated on the authority of Umm Sinaan Al-Ansaariyyah 
who said that the Prophet, sallallaahu ‘alayhi wa sallam said, "‘Umrah in Ramadan is equivalent (in reward) to a Hajj that is performed with me." [Al-Bukhari and Muslim]
It is not necessary to wait until midnight because the night of the first of Ramadan starts at sunset of the day that precedes it.