[Christian]

Being paranoid about missing an action I sometimes just set the starting date to be like a week or few days before the action does actually become availible in the real world. In your case that would mean that you might set the start date for the "waiting for customer" action to the 10th of April. The wedding may be on the 15th, you might send the pictures to the customer on the 16th and then have to wait. But when you prepare for the project "shoot wedding" on the 12th you can already see which actions are going to be necessary and hence have a good feeling of complete overview.