Some say early morning, some say mid morning before the tourist buses arrive, some say during lunch time, some say in the afternoon when people are already leaving. The truth is, the Alhambra is busy the whole day and there isn’t much difference from one time of the day to another.
There is a limited number of tickets sold per day and a limited number of 30-min slots for the Nasrid Palaces – once they’re booked up, that’s it. That means if you book for say 10:00am at the Nasrid Palaces and the time slot is full, then you will have the same amount of people as the 2:00pm slot that is also full.
If your priority is to see the architecture and take photos then the biggest factor is the time of year you visit, not the time of the day. Taking in the details of the palaces and snapping photos is definitely easier when you don’t have so many people around.
The winter months are your best bet in such cases. November to February have significantly fewer visitors than other times of the year. However, if you want to see the gardens in full blossom then you are going to have crowds – there’s just no way to avoid it.