It gets quite hot in the summer, so be sure to bring lots of water. If you're planning on walking, wear comfy shoes. It's possible to grab a taxi at any point if you're feet get sore or tired.
Start this first thing in the morning and beat the heat of the day. The mosque opens at 8am and is quiet in the morning.
July and August are incredibly hot, but the winter can get a bit chilly. The best time to visit is May-June and September-October.
The entrance fees and taxi fare are very inexpensive.