The period when I was here, from late July to early August, can be seriously hot. The government even announced a heat wave warning. So my recommendation is to come during spring, which is between April and June. September’s cooling weather is great too.
If you’re here in July like me, make sure you bring lots of sunblock and aloe vera gel to defend yourself against the merciless sun! You can barely open your eyes if you don’t wear a cap, the sun was just so glaring.