Scenario 1: BC was not done during the night of the 14th and is now being done during the day – i.e. Erev Pesach in the morning.
BC should be done as early as possible and before one eats that morning! If one is checking outside in the daylight, in a place where there are no “shadows”, such as in dark nooks and crannies, it is sufficient to use the natural daylight. If there are shadows or when checking indoors (even with light streaming in through window panes), a candle must be used!
Scenario 2: BC was done at night properly with a candle, but a day early – the night of the 13th. If one was careful not to bring in any more chametz after his search, a full 2nd BC is not necessary on the night of the 14th; however, he should do BC in a token room in his house (or on some other property of his), in order to fulfill the mitzvah in its proper time. If he was not particularly careful about chametz, then he must conduct another full BC on the night of the 14th. In these cases, one should not make a bracha on the 2nd BC. If possible, he should be ‘yotze’ with the bracha of another person.
Scenario 3: BC was done on the day of the 13th (i.e. only hours before the proper time).
This BC is not as effective, b’diavad, as the one in scenario 2, because he did not search at night with a candle. Therefore, he must search again at night (i.e. the whole house - even if he was careful not to bring in any chametz), but still without a bracha (because his search still accomplished something!) Of course, as we learned with scenario 1, any searching that he did outside in the daylight without shadows counts completely (b’diavad) and he need not search there again.