It can take anywhere from 4-5 days up to a few weeks before you will notice signs of flowering beginning. It depends heavily on the genetics, and the maturity of the plant. An immature plant can take weeks to begin flowering.
Your environment can also affect things. Cold conditions can slow down the growth processes of the plant for example. I had completely mature clones that normally would take 5ish days to show flowers take 3 weeks because of a cold snap one winter. After I fixed the temps the plants finished completely normally just delayed by 3 weeks.
