We are planning to visit in late May 2018. My two main questions are how much time to set aside for the Alhambra sights and is there a suggested time of day to make reservations. Our daughter recommended late in the day to avoid mid-day heat. Thanks.
First of all , make certain that you book your entrance to The Nasrid Palace as soon as possible ( usually about 90 days ahead ) . I booked a very early entrance ( 8:30 AM ) the crowds were light , and we had adequate time to enjoy the palace . While the heat in Spain was high ( Late September ) , rest of the complex and particularly The Generalife Gardens were fairly pleasant due to the elevation above Granada and a light breeze coming from the surrounding mountains .
The Alhambra website is currently showing no tickets available for May 1 and "Last Tickets" available for the rest of the month. Do not wait too long.
I would advise booking the Nasrid Palaces as soon as it opens, otherwise the crowds are oppressive. Entry times are strictly enforced. We saw several groups turned away, because they arrived 30 minutes past their assigned time. We spent between 4-5 hours total at Alhambra. Totally agree with the previous poster's advice to purchase your tickets as soon as your dates are firm because they will sell out. Enjoy!