A Muslim is always encouraged and required to keep asking Allah and making du`a with all his needs at all times. The Prophet (peace and blessings be upon him) directed us to seek and du`a at certain times in which du`a is most likely to be answered.
However, one should be aware that answering his/her du`a in the way he/she sought is not necessary. Peoples’ wishes cannot change the divine predestination. In an authentic hadith the Prophet (p.b.u.h.) stated that when a Muslim makes du`a, he/she gains one of three things: either his/her du`a is answered or something evil is turned away from him/her instead or he/she gets a reward in the Hereafter.