Although the issur of chometz does not begin before the seventh halachic hour on the fourteenth day. Nevertheless, Chazal held that the search must be done in the evening for two reasons.
Most people are at home in the evening.
One may not engage in one of the above within a half an hour before the time of bedikas chometz. The reason for this is that Chazal were afraid that one would become engrossed in the subject matter and become negligent and not perform the bedika in its proper time. If one started within the half an hour, one must stop what they are doing and perform the bedika. B'halacha 111-3, Divar Yehoshua Vol. If a person goes away from home more than thirty day before pesach but intends to return before pesach, one must perform the bedika before they leave without a bracha.