A gardener wants to model the number of hours of daylight his allotment receives at different times of the year using a function of the form
where is the number of hours of daylight on a given day, is the time measured in whole days, and and are positive constants. Note that corresponds to the first day of the model.
(i) Given that the model needs to predict a maximum of 17 hours daylight and a minimum of 7 hours daylight, find the values of and .
(ii) Explain the significance of the value in the model.
(iii) Suggest, with a reason, the date of the year that the model starts on.