But, when such a plan of tribal numbering was adopted, the time of the year had to be carefully considered. In the first place the winter months had to be avoided, during which travelling was often difficult, and in which unfavourable weather might cause great hardship and even prevent the plan from being carried out. As the day had to be fixed a long time beforehand, it must have been fixed in the season when good weather could be calculated on. In winter, weather might be good or it might be bad, and at the best it would be cold and trying.
Further, it was urgently necessary that the time which was fixed should not interfere with agricultural operations- that it should not come between the earliest date for the first harvest and the latest date for finishing the threshing, and getting in the grain and the fine cut straw from the threshing floors. The harvest varied considerably in different parts of the country, and reaping extended over about seven weeks, beginning from the middle of April.
Taking these circumstances into consideration, we may say with considerable confidence that August to October is the period within which the numbering would be fixed. It is no objection to this view that tradition places the birth of Jesus at Christmas. It is well known that the tradition is not early, that it varies in different periods and in different sections of the Church, and that the earliest belief was different.
from pages 192-193, Was Christ Born in Bethlehem?