Multan is famous across Pakistan for four things: dust, heat, beggars and graveyards — gard, garma, gada, gauristan — and the first two are a real consideration. From mid-April to late September daytime temperatures regularly pass 45°C, and in May and June can hit 50°C with humid pre-monsoon haze. Walking the fort or the bazaars is genuinely unpleasant; locals reschedule their lives around it, working from 5am and again after sunset.
The comfortable season runs from late October to early March, with cool nights, dry sunny days in the high teens to mid-twenties, and crisp morning mists off the Chenab. November is particularly good: the urs of Bahauddin Zakariya falls in this month and brings thousands of pilgrims and several days of qawwali music to the fort. February and March are warm but still pleasant, with the spring basant kite-flying season at its peak. Avoid June, July and August unless you have no choice.