There are always four candy bombs on the board and they have 9-move fuses. If you clear any of them more will spawn next move.
SO once they are in matchable positions, let them count down as low as possible while making matches elsewhere on the board, especially the green and purple candies to fill the order.
Match the bombs only when absolutely necessary, at 1 or 2 moves before they go bang, in this way you will not spend the whole time fighting bombs and not filling your order.
If you cannot make a match to fill the order, while the bombs are ticking away, make intelligent matches elsewhere on the board to clear out the useless colours and let more green and purple candies fall.