Block trade

I read that in a block trade, that the sales trader contact other institution in order to match the order of his client in a cross trade. I read also that after found their counterparties, they enter their respe tive order in the same time in the market. What i don t see is how they do this? They say that for exemple at 3 pm we enter the order? And if they do this at the same time, how the market is taking this? As a buy or a sell? So price is going up or down?