When does the bouquet throw happen?
It can happen at any time. It's a quick little fun set-up. It doesn't have to precede or follow anything.
It's something worth considering, just don't think about the florists bill when you do it. I had a pre-wedding meeting once and I asked this question. The bride answered 'No chance!' Her reason for such a strong responce was because minutes before I'd rang the door bell, she'd had written out a cheque for her florist.
Just pinch one from your bridesmaid.