When does the waiting period for a mother (widow) end if her husband died on 18 Rabee' Al-Aakhar 1430 AH, corresponding to 13/4/2009, at 5 AM?

Your mother's 'iddah (waiting period) begins on the 18th of Rabi' al-Akhir at the exact time of your father's passing. She will complete the month of Rabi' al-Akhir and three lunar months thereafter (Jumada al-Ula, Jumada al-Akhirah, Rajab). Then, she will complete from Sha'ban whatever makes Rabi' al-Akhir a full thirty days. By doing so, she would have completed four months. To this, she adds ten days, ending at the exact same time your father passed away.