if its the same as last year i think there was a delay of around 7 minutes between it happening and it being shown on tv giving them time to censor anything they arent allowed to broadcast.
Sometimes I think they 'cover up' certain dialogue that is going to feature in that evening's BB prog at 9.00p.m. They want to keep it 'fresh' so that nothing 'leaks' out before the main prog. Don't know if this is true or not but it seems feasable