If you would like to select a certain day and it is quite in advance (more than a week) then we require some form of a deposit. This protects us from missing out on other work, as we would turn others away who potentially would use us on that day. The likelihood that no one can help you in slim, so don’t worry, it’s doubtful there will be no capacity at all. Moreover, weather plays such role that it is better not to be so adamant to stick to one day.
Just mail us if you have any more questions regarding this.