The best time to visit Srirangam is between October and March, when temperatures are bearable (25–32°C) and humidity is lower. Avoid May and June, when temperatures regularly exceed 40°C — the temple complex involves extensive walking on stone and open courtyards that reflect and retain heat.
The Vaikunta Ekadasi festival in December is the major pilgrimage event at the Ranganathaswamy Temple, drawing hundreds of thousands of pilgrims over several days. The atmosphere is extraordinary but the crowds are intense. The temple opens the Paramapada Vasal gateway — the "Gate of Heaven" — only on this occasion once a year, and pilgrims believe that dying while passing through this gate leads directly to liberation. If you want to experience the temple at its most alive, this is the time to go; if you want space to look at the architecture, come in a quieter month.